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http://www.archive.org/details/textbookofhistoOOst 


TEXT-BOOK 

HISTOLOGY 


STOH  R 


TEXT-BOOK 


H  ISTOLOGY 


INCLUMINi; 


THE    MICROSCOPICAL  TECHNIQUE 


DR.    PHILIPP    STOHR 

rtlCAL   INSTITl'TR    IN    ZURICH 


SIXTH   EDITION 

rRANSLATEI)    U\   KMMA   L.   BILLSIEIN,   M.  D. 

i;i)l  IKI),  WITH    ADDITIONS 

11 V 

DR.   ALFRED    SCHAPER 


TlGitb  20S  Ullustvations 


I'HII.ADKLI'HIA 

I',    i;  1.  .\  K  1  S  T  O  N,    so  X     c\:    C  O 

I  O  1  2     W  A  I.  .N  U  r     S  l'  K  H  K  1' 

1  s'.m; 


CoPYKinHT,  1896,  BY  Dr.  Alfred  Schapek. 


Press  of  Wm.  F.  Fell  &  Cc 

1220-24  SANSOM  ST.. 


EDITOR'S    PREFACE. 


Stiihr's  text-book  is  well  known  to  the  histologists  of  all  nations  and  held 
in  high  esteem  by  them.  To  the  German  medical  student  it  has  become  an  in- 
dispensable guide.  During  the  ten  years  of  its  existence  it  has  reached  an  ex- 
traordinary sale  and  pa.ssed  through  six  revised  editions.  It  has  been  translated 
into  Italian  (1887),  French  (1890),  and  Russian  (1891),  and  has  thus  come 
into  the  hands  of  the  students  of  these  nations.  These  facts  are  sufficient  to 
guarantee  the  value  of  the  work  without  further  recommendation,  .\lthough 
excellent  text-books  of  Histology  already  exist  in  English,  still  the  peculiarity 
and  special  superiority  of  Stohr's  text-book  justifies,  in  our  opinion,  its  transla- 
tion into  English  for  the  convenience  of  .\merican  and  English  students.  * 

It  is  especially  intended  for  the  use  of  students,  but  even  professional  histol- 
ogists and  physicians  will  find  in  it  much  valuable  information,  as  well  as  sug- 
gestions for  technical  purposes.  The  chief  merit  of  the  work  lies,  on  the  one 
hand,  in  the  brevity  and  perspicuity  of  the  descriptive  text,  elucidated  by 
illustrations  which  have  thus  far  never  been  excelled  ;  and,  on  the  other  hand, 
in  the  simplicity  and  certainty  of  the  methods  for  preparing  the  most  important 
microscopical  specimens.  The  young  .student  is  thus  enabled  to  practice 
histological  methods  privately,  at  a  minimum  cost,  in  connection  with  his  courses 
in  the  university.  The  preparation  of  almost  all  of  the  specimens  enumerated 
in  the  book  can  be  made  simply  by  means  of  teasing,  isolation,  or  cutting  with 
the  razor,  but  those  .students  who  have  a  microtome  at  their  disposal  will  also 
find,  in  an  .\|)pendix,  brief  directions  tor  the  preparatory  treatment  (embedding 
in  paraffin  and  celloidin)  of  specimens  for  sectioning  with  the  microtome. 

With  the  permission  of  Prof.  Stohr  we  have  made  several  immaterial,  but  for 
an  American  edition  very  desirable,  changes  in  the  text,  and  have  considered 
it  more  preferable  to  place  the  technical  part  as  a  whole  at  the  end  of  the 
book  rather  than  in  sections  after  the  several  chapters.  Furthermore,  we  have 
enlarged  the  cha])ter  on  the  I'terus,  in  order  to  give  detailed  consideration  to 
the  various  functional  conditions  of  the  organ,  and  added  to  the  book  an 
entirely  new  chapter  on  the  I'lacenta.  Eight  new  illustrations  (Fig.  200,  201, 
202,  203.  204,  205,  206,  207)  were  neces.sary  for  these  additions. 

*  In  1888  Stohr's  Text-book  was  utilized  in  Kendrick's  Physiology,  but  in  such  a  frag- 
mentary form  and  so  intermingled  with  selections  from  other  .luthors  thai  its  chief  merits  wero 
entirely  lost.     This  use  of  the  book  cannot  be  considered  as  an  Knglish  translation  proper. 


VI  EDITOR  S    PKEFACK. 

The  editor  is  under  great  obligation  to  the  translator,  Dr.  Billstein,  for 
her  successful  efforts  in  reproducing  the  conciseness  and  clearness  of  the  German 
original.  Further,  he  desires  to  express  his  gratitude  to  Professor  Philipp  Stohr 
for  placing  at  his  disposal  the  original  electrotypes,  and  to  Drs.  Bohm  and  von 
Davidoff  for  the  illustration  of  the  virginal  uterus  (Fig.  200)  from  their 
"  Lehrbuch  der  Histologic."  He  also  feels  deeply  indebted  to  Professor 
Charles  S.  Minot  for  kind  assistance,  valuable  criticism,  and  for  permission 
to  use  two  illustrations  (Fig.  202  and  205)  from  his  text-book  of  "Human 
Embryology  ";  and  finally  to  Messrs.  P.  Blakiston,  Son  &  Co.,  Philadelphia,  for 
the  very  satisfactory  reproduction  of  the  new  drawings,  and  for  their  many 
courtesies  during  the  preparation  of  the  American  edition. 

Alfred  Schaper. 
Harvard  Medical  School, 
Boston,  Juiii,  iSgb. 


CONTENTS. 


PART  I. 


GENERAL    TECHNIQUE. 


The  Labokatiiky  Ai'coint- 

MENTS 

Instrumenls. 
Reagents. 

The  Pkei'akation   ok   Mi- 
(_'Rosci)i'iCAi. Specimens,  . 

Introduction. 

Nature  of  the  Materia). 

Killing  and   Dissecting  tlie 
Animals. 

Isolating. 

Fixation, 

Hardening, 

Decalcifying. 


The  Preparation  of  Microscopical  Speci-      r^cK 
mens. — Continued. 

Sectioning. 

Staining. 

Injecting, 

Mounting   and    Preser\ing  of 
the  I'reparations. 

Examination  of  Fresh  Objects. 

Storing  of   I'ermanent  Speci- 
mens, 

III.  Management  ok  the  Micro- 
scope,        43-46 

Drawing, 
Measurement. 


PART  II. 

MICROSCOPICAL    ANATOMY. 


I,   }llsTOl,oi;v. 

A. — Cells 4X-54 

Parts, 

Form, 

Size. 

Vital  Properties. 

Phenomena  of  Motion. 

Reproduction  and    Multi- 
plication. 

Phenomena  of  Secretion, 

Length  of  Life. 

Growth, 

Secretory  Products. 
H. — Tissues, 

The  Epithelial   Tissues,  .       55-63 
Secretory  .-Xctivitv. 


Histology. — Continued. 

The  Glands. 
The  Connective    Tissues,       64-72 

Connective  Tissue, 

Cartilage, 

Bone. 
The  Muscular  Tissues,    ,       72-76 

Involuntary. 

Voluntary, 
The  Nervous  Tissues,     .       76-.S3 

Nerve-Cells. 

Nerve-Fibers. 

II.    MlCROSCOrlCAl,        .\NATOMV 

OF  THE  Organs. 
The  Circulatory  System,      ,    ,       S4-93 


CONTENTS. 


Microscopical     Anatomy    of    ilie 
gans.  —  Coiitinitc'i/. 
The  Heart. 
Tlie  Arteries. 
The  Veins. 
The  Capillaries. 
The  Blood. 
The  Lymphatic  System, 
The  Lymph-vessels. 
The  Lymph-nodes. 


The    *  >rgans    of    the    Nervous    Sys- 
tem. — Contitiued. 
The     Peripheral     Nerve 
Endings. 
Terminations    of   Sei-.- 

sory  Nerves. 
Tactile-Cells. 
End-Bulbs. 
Terminations  of  Motor 

Nerves. 


The  Peripheral    I.ympli- 

The  Suprarenal  Body.     .    .    . 

U3- 

144 

nodules. 

The  lA-raph. 

\1.  The  DiGESTixE  Orc;.\n>.     . 

.  14-;- 

I.S4 

The  Spleen. 

Mucous  Membranes. 
The  Teeth. 

111. 

The  Org.\ns  of  tiik,  Skki.i-,- 

ialSystkm 100-113 

The  Bones. 

The  Articulations. 
The  Cartilages. 
Development  of  Bone. 
Development  of  Primary 

Bone. 
Secondary  or   Intt-i mem- 

The Tongue. 
The  Pharynx. 
The  Esophagus. 
The  Stomach. 
The  Intestines. 
The  Salivary  Glands. 
The  Liver. 
The  Peritoneum. 

branous  Bone. 

Vn.  The  Kesi'Iratory  Organs. 

I,S4- 

lot 

IV. 

The  Oko.w.s  of  the   Mi  ^- 

em,.\R  System ii.s-iiS 

The  Muscles. 
The  Tendons. 
The  Fascix. 

The  Larynx. 
The  Trachea. 
1                  I'he  Bronchi  and  the  1  .ung>. 
The  Thyroid  Gland. 
The  Thymus  Body. 

The  Organs  of  iiie  .\],k- 

vous  System. 
The  Central  Nervous  System.  116-134 
The  Spinal  Cord. 
Topography. 
Mmute  Structure. 
The  Brain. 

The  Cerebrum. 

The  Cerebral  Ganglia. 

The  Gray  Substance  of 

the  Ventricles. 
The  Cerebellum. 
The  Membranes  of  the 
Central  Nervous  Sys- 
tem. 
The  Blood-vessels  of  the 
Central    Nervous  Sys- 
tem. 
The  Peripheral  Nervous  Sys- 

tem, 134-14.1 

The  Nerve  Trunks. 
The  Ganglia. 


VIU.  The  Urinary  Organs,     .    .  191-198 
The  Kidneys. 
The  Ureters. 
The  Urinary  Bladder. 
The  I'rethr.n. 

IX.  The      Rei'RoiU'I  rivE     Or 

GANS, icjS-223 

The    Male    Reproductive  Or- 
gans. 

The  Testicle. 
The  Semen. 
The   E.xcretory   Ducts  of 

the  Testicle. 
The  Prostate  Body. 
The  Penis. 
The  Female  Reproductive  Organs. 
The  Ovaries. 
The  Oviduct. 
The  Uterus. 
The  Placenta. 
The  Vagina  and  the  Genitali.T. 


CONTENTS. 


X.  TiiK  Skin  and  its  Ani.Ni>         ■'*<;'' 

AGES, 223-236 

The  Skin. 

The  Nails. 

The  Hair. 

The  Glanils  of  the  Skin. 

The  Bloodvessels,  Lymph- 
Vessels,  and  Nervrs  of  the 
Skin. 

The  Manimarv  (iland. 


The  Eyk  anh  iis  Aithnd- 

.v;ks 23I1-259 

The  Eyeball. 

The  Tunica  liMerna. 
The  Tunica  Media. 
The  Iridocorneal  .Angle. 
The  Tunica  Interna. 

The  Cerebral  Layer. 
The     Neuro-Epitlielial 
Layer. 
The  Optic  Nerve. 
The  Lens. 
The  Vitreous  Body. 
The  Suspensory  Ligami-ni. 


The  Eye  and  its  .Appendages. — Con-  fack 

tiniifii. 
The    Blood  ■  \'essels    of    the 

Eyeball. 
The    Lymph-Channels  of  the 

Eyeball. 
The  Nerves  of  the  Eyeball. 
The  Eyelids. 
The  Lacrymal  Glands. 

Ml     Tim    Organ  df   Hkakinh,  .  260-269 
The  Internal  Ear. 
The  .Saccule,  The  Utricle,  and 

the  Semicircular  Canals. 
The  Cochlea. 
The  Middle  Ear. 
The  External  Ear. 

XIII.  The  Nasal    Mucuih  Mkm- 

BRANE, 26()-27; 

The  Vestibular  Region. 
The  Respiratory  Region. 
The  Olfactory  Region. 

XIV.  TlIF,  TaSTE-HL'DS 27^-27S 


PART  III. 

SPfEClAL    TKCHNIQUE. 


I.   Karyokinesis 

II.    Cll.I.\TED    Er  1  T  II  K  I.  I  A  1. 

Cells 

Connective-Tissue.  .    .    . 

Muscle-Fibers 

Nerve-Cells  and  Nerve- 
Fibers,     

The    Heart    and     the 
b1.00d-vessei.s,     .    .    . 

The  Blood, 

VIII.  The  Lymphatic  System, 
IX.  Bone, 


III. 
IV. 
V. 


VII. 


277 

277-279 

279-280 


2S0-282 


X. 

\1. 


Muscles  and  Tendon,     . 
The  Organs  of  the  .Ner- 
vous System 


282-284 
284-287 
287-289 
289-292 
292-293 

293-300 


XII.    Ihe  Digestive  Tkact,     . 

XI II.  The     Respiratory     Or- 

gans,     

XIV.  The  Urinary  Organs, 
XV.  The   Testicle    and    the 

Ovary, 

XVI.    The  Skin  and  its  .Append- 
ages,      

XVII.    I'he  Eve  and  its  Append- 


308-310 


-Will.    The  Organ  ok  Hearing, 

\I\.    The   Mucous   Membrane 
ciFTiiE  Nose 


APPENDIX. 


M  iCROTO.\iK  Tech  n  njf  e. 


.  326-330       Preservation  of  Secfions 


LIST  OF  ILLUSTRATIONS. 


1.  I.eitz  Microscope .    .  44 

2.  Diagram  of  a  Cell, 49 

3.  Cell  of  Bone-Marrow  of  Rabbit, 50 

4.  Leucocyles  of  Frog, 5° 

5.  Karyokinelic  Figures — Epithelium  of  Salamander, 5^ 

6.  Epithelial  Cells  of  Ral)bit.  Isolated, 55 

7.  I'rickle-Cells  of  Stratum  Mucosum  of  Epidermis .  5*^ 

8.  Pigmented  Epithelium 56 

9.  Simple  Columnar  Epithelium 56 

10.  Stratified  Sc|uamous  Epithelium, 57 

11.  Stratified  Ciliated  Epithelium, 57 

12.  Secreting  Epithelial  Cells, 5*^ 

13.  Crypt  of  I-ieberkiihn, 59 

14.  Diagram  of  the  Different  Gland  Forms,            60 

15.  Section  of  Mucous  Glands  of  Tongue  of  Rabbit .        62 

16.  Section  of  Fundus  Gland  of  Mouse, 62 

17.  Diagram  of  Origin  of  Crescents, 63 

18.  Cross-Section  of  Umbilical  Cord  of  Human  Embryo, 64 

19.  Connective-Tissue  Bundles 64 

20.  Elastic  Fibers 65 

21.  Network  of  Elastic  Fibers, 65 

22.  Connective-Tissue  Cells,  Bundles  of  Connective-Tissue  Filers 65 

23.  Fat-Cells, 66 

24.  Reticular  Connective  Tissue 67 

25.  Hyaline  Cartilage, 68 

26.  Elastic  Cartilage, 69 

27.  Section  of  Intervertebral  Disk  of  Man, 70 

28.  Ground  Section  of  Dried  Bone  of  Adult  Man 70 

29.  Sections  of  Humerus  of  Human  Embryo,  and  of  middle  Turbinal  of  Man,        .    .  70 

30.  Section  of  Diaphysis  of  Humerus  of  Human  Embryo 71 

31.  Smooth  Muscle- Fibers  from  Small  Intestine  of  Frog 72 

32.  Section  of  Circular  Layer  of  the  Muscular  Coat  of  Intestine 73 

33.  Muscle- Fibers  of  Man 74 

34.  Isolated  Striated  Muscle- Fibers  of  Frog 75 

35.  Muscle-Fibers  of  Heart 7'> 

36.  Diagram  of  a  Neuron, 77 

37.  Various  Fonns  of  Ganglion-Cells 78 

38.  Nerve-Cell 79 

39.  Nerve-Cells  from  the  Spinal  Cord  of  Embryo  Chick 80 

40.  Teased  Preparation  from  the  Sympathetic  Nerve  of  Rabbit,      .        .             Si 

41.  Medullated  Nerve- Fibers 82 

42.  Medullated  Nerve-Fibers,  Treated  with  Silver  Nitrate  Solution.        .  S3 


XU  LIST    OF    ILLUSTRATIONS. 

43.  Section  of  Papillary  Muscle  of  Human  Heart 84 

44.  Small  Arteries  of  Man, 85 

45.  Cross-Section  of  Brachial  Artery  of  Man, ...  86 

46.  Endothelium  of  Mesenteric  Artery  of  Rabbit,         87 

47.  Cross- Section  of  Thoracic  Aorta  of  Man,         87 

48.  Cross-Section  of  Vein  of  Man,                   88 

49.  Cross-Section  of  Renal  Vein  of  Man, Sg 

50.  Surface  View  of  tlreater  Omentum  of  a  Seven-Days'-Old  Kabliit 90 

51.  Blood  Corpuscles 91 

52.  Colorless  Blood-Cells  of  Man, .    .  92 

53.  Hemin,  Hematoidin,  Hemoglobin  Crystals;   Crystals  of  Common  Salt, 93 

54.  Lymphatic  Vessel  of  Mesentery  of  Rabbit,      94 

55.  Section  of  Lymphatic  Nodule  of  Nine-Days'-Old  Cat 95 

56.  .Section  through  Medulla  of  Lymphatic  Nodule  of  Ox,       96 

57.  Cross-.Section  of  Human  Spleen, 97 

58.  Elements  of  Human  Spleen,          98 

59.  Reticular  Connective  Tissue  of  Humnn  .Spleen ....  98 

60.  Three  Karyomitotic  Figures  from  Sjileen  of  Dog,    .             98 

61.  Section  of  .Spleen  of  Mouse, 98 

62.  A.  Section  of  Injected  Spleen  of  Cat, 99 

62.  B.   Schematic  Drawing  of  Section  62,  A.      .. 99 

63.  Longitudinal  Section  through  Human  Metacarpus,      .    .  

64.  Cross-Section  of  Metacarpus  of  Man 

65.  Elements  of  Human  Bone-Marrow   ... 

66.  Cross-Section  of  Femur  of  Adult  Man 

67.  Section  through  Head  of  Metacarpus  of  Adult  Man 104 

68.  Synovial  Villi  with  Blood-Vessels  from  Human  Knee-joint 106 

69.  Section  of  Oreat  Toe  of  Human  Embryo, 107 

70.  Section  of  Finger  of  Human  Embryo, loS 

71.  Section  of  Phalanx  of  First  Finger  of  Human  Embryo, tog 

72.  Cross-Section  of  U|iper  Half  of  Diaphysis  of  Humerus  of  Human  Embryo.     .    . 

73.  Cross-Section  of  Lower  Jaw  of  Newborn  Dog 

74.  Section  of  Parietal  Bone  of  Human  Embr)0, 

75.  Cross-Section  of  Humerus  of  Newborn  Cat •    . 

76.  Cross-Section  of  Adductor  Muscle  of  Rabbit, 

77.  Cross-Section  of  Dried  Tendon  of  Adult  Man 114 

78.  Tendons  from  Rat's  Tail 115 

79.  Section  of  Gastrocnemius  of  Frog 115 

So.   Cross- Section  of  Cervical  Enlargement  of  Human  Spinal  Cord,  .    .     ■ 117 

81.  Cross-Section  of  Spinal  Cord  of  Embryo  Chick, 

82.  .Scheme  of   Spinal  Cord,  showing  the  Nerve-Cells,     .        .  

83.  Longitudinal  .Section  of  Spinal  Cord  of  Newborn  Rat. 

84.  Cross- Section  of  Spin.al  Cord  of  Newborn  Rat 

85.  Glia-Cells  from  Spinal  Cord 

86.  Cross-Section  of  Human  Spinal  Cord,  

87.  Section  of  Human  Cerebral  Corte.t, 124 

88.  Scheme  of  Cerebral  Cortex, 124 

89.  Pyramidal  Cell  from  Cerebral  Cortex  of  .^dult  Man, 125 

90.  Glia-Cells  of  Human   Brain, 126 

91.  Section  through  Cortex  of  Cerebellum  of  Adult  Man.        .    .        127 

92.  Small  Granule-Cell  from  Cerebellum  of  Cat 1 28 

93.  Large  Granule-Cell   from  Cerebellum  of  Cat, 128 

94.  Scheme  of  Cerebellar  Cortex .        


LIST    OK    ILI.U.STRAI  IONS.  Xlll 

10.  PAGE 

95-  Basket-Cell  from  Cerebellar  Cortex  of  Cat,      . 1 50 

96.  Section  of  Cerebellar  Cortex  of  Adult  Man ...  131 

97.  GliaCells  from  Cerebellar  Cortex  of  .\tluli  Man 132 

98.  Section  of  Human  Pituitary  liody, 132 

99.  Acervulu.s  Cerebri  from  I'ineal  Body, •    .■    •  '33 

00.  Gray-Sul 'Stance  from  \V;iIi  of  a  Ventricle  of  Human  Br.\in 133 

01.  Cross-Section  of  Human  Median  Nerve,  X  20, 135 

02.  Cross-Section  of  Human  Median  Nerve,  X  220,         135 

33.  Cross  Section  of  the  Gasserian  Ganglion  of  Man 136 

04.  Section  of  the  Superior  Cervical  Ganglion  of  .Man 137 

05.  Section  through  Skin  of  Great  Toe  of  Man,         138 

06.  Section  through  Skin  of  Great  Toe  of  Man,  showing  Tactile-Cells,      .    .  139 

07.  Section  through  Skin  of  Beak  of  (ioose, 139 

08.  Cylindrical  Knd-Bulb  from  Conjunctiva  of  Calf,      ...         ,    .     .    ,  140 

09.  Small  Corpuscle  of  Vater  from  Mesentery  of  Cat, 140 

10.  Tactile  Corpuscle  from  Great  Toe  of  Man 141 

11.  Motor  Nerve-Ending  of  Intercostal  Muscle-Fibers  of  Rabbi- 142 

12.  Motor  Nerve-Ending  in  a  Fiber  of  an  Ocular  Muscle, 142 

13.  Section  of  Suprarenal  Body  of  Child, 143 

14.  Section  of  Mucous  .Membrane  of  I.ip  of  .Adult  Man,     .    .             145 

15.  Section  of  Human  Tooth 146 

16.  Section  of  Lateral  Part  of  Crown  of  Human  Molar  Tooth ...  147 

17.  Section  of  Fang  of  Human  Molar  Tooth 147 

18.  Section  of  Tooth  of  Infant, t|7 

19.  Odontoblasts  with  Dentinal  Fibers, 14S 

20.  Scheme  of  the  Initial  Processes  in  the  Development  of  the  Teeth,  149 

21.  Frontal  Section  of  Head  of  Embryo  Sheep, .149 

22.  Cross- Section  of  Lower  Jaw  of  Human  Embryo, 150 

23.  Cross-Section  of  Upper  Jaw  of  Human  Embryo, 151 

24.  Section  of  Voung  Milk-Toolh  of  Newborn  Dog 152 

25.  Section  of  Mucous  Membrane  of  Dorsum  of  Human   Tongue,                                   .    .  153 

26.  Section  of  Mucous  Membrane  of  Human   Tongue,          ...  153 

27.  Section  of  a  Circumvallate  Papilla  of  Man, 154 

28.  Section  of  Lymph- Follicle  from  Root  of  Human  Tongue.                              155 

29.  Serous  Gland  of  Root  of  Tongue  of  Mouse 155 

30.  Section  of  Mucous  Gland  of  Root  of  Human  Tongue,       156 

31.  Cross-Section  of  Middle  Third  of  Human  Esophagus,       15S 

32.  Transverse  Section  of  Human  Stomach I5<S 

^T^.  Section  of  Mucous  Membrane  of  Cardiac  End  of  Human  Stomach,    ....  159 

34.  Section  of  a  Human  Fundus  (iland,          ... ibo 

35.  Cross-.Section  of  Mucous  Membrane  of  Fundus  of  Stomach, 161 

36.  Ixjwer  Portion  of  a  Pyloric  Gland 162 

37.  Section  of  Jejunum  of  Adult  Man 163 

38.  Section  of  Mucous  Membrane  of  Jejunum  of  .\duli  Man 164 

39.  Intestinal  Epithelium ...  164 

40.  Section  of  Ape.x  of  a  \'illus  of  Dog,     . 165 

41.  Section  of  Duodenum  of  Cat 166 

42.  Section  of  a  Patch  of  IVyer  of  Small  Intestine  of  Cat, 167 

43.  Section  of  Small  Intestine  of  Kitten,  Showing  Crest  of  a  Solitary  Follicle 167 

44.  Section  of  Injected  Small  Intestine  of  Rabbit,         .    .              16S 

45.  Plexus  of  Auerbach  and  of  Meissner,           170 

46.  Section  of  Human  Sulilingual  (iland 171 

47.  Section  of  Human  Parotid  Gland,  .172 


LIST    OF    ILLUSTRATIONS. 


148.  Section  ol"  Human  Submaxillary  Gland 172 

149.  Gland-Cells  of  Pancreas — Section  of  Pancreas  of  Infant, 172 

150.  Section  of  Pancreas  of  Adult  Man, 173 

151.  Section  of  Submaxillary  Gland  of  Dog,    ...         173 

152.  Scheme  of  Hepatic  Lobule, 174 

153.  Liver-Cells  of  Man, 175 

154.  .Section  of  Human  Liver, ....  175 

155.  Section  of  Liver  of  Dog 176 

156.  Bile  Capillaries,  Liver  of  Dog 177 

157.  Section  of  Injected  Liver  of  Rabbit, 178 

158.  Section  of  Injected  Liver  of  Cat 178 

159.  Section  of  Injected  Liver  of  Cat,      179 

160.  Section  of  Injected  Liver  of  Rabbit, 179 

161.  .Scheme  of  an  Ordinary  Gland-Tubule  and  of  a  Hepatic  Tubule 180 

162.  Section  of  Liver  of  Rabbit,  with  Injected  Bile-Capillaries, 180 

163.  Section  of  Human  Liver, 181 

164.  Scheme  of  a  System  of  Excretory  Channels, 181 

165.  Scheme  of  the  Liver 182 

166.  Scheme  of  Transverse  Section  of  Liver, 1 82 

167.  Greater  Omentum  of  Rabbit 183 

168.  Cross-Section  of  Bronchus  of  Child,          l86 

169.  Section  of  Lung  of  Adult  Man 187 

170.  Sections  of  Human  Lung  and  of  Kitten's  Lung 187 

171.  Section  of  Injected  Lung  of  Child, 189 

172.  A  Lobule  of  Thyroid  Body  of  .\dult  Man, 1S9 

173.  Section  of  .Secondary  Lobules  of  Thynvus  Body  of  Rabbit 190 

174.  Corpuscle  of  Hassall,      190 

175.  Scheme  of  the  Course  of  Uriniferous  Tubules  and  of  Renal  Blood-Vessels,    ....  192 

176.  Uriniferous  Tubules  of  Rabbit, 192 

177.  Section  of  Human  Kidney I93 

178.  Scheme  of  Malpighian  Corpuscle  of  Kidney 193 

179.  Section  of  Kidney  of  Mouse 194 

180.  Isolated  Cell  and  Section  of  Convoluted  Tubule  of  Kidney 194 

181.  Section  of  the  Medulla  of  Human  Kidney, 194 

182.  Section  of  Injected  Kidney  of  Guinea-Pig, 195 

183.  Section  of  Kidney  of  Mouse 195 

184.  Section  of  Lower  Half  of  Human   Ureter, 196 

185.  Section  of  Human  Vesical  Mucous  Membrane 197 

186.  Section  of  Testicle  of  a  Newborn  Child, 199 

187.  Section  of  Testicle  of  Ox 200 

188.  Section  of  a  Seminiferous  Tubule  of  Mouse, 201 

189.  Human  Spermatozoa,       202 

190.  Section  of  an  Adult  Human  Vas  Efferens  Testis, 203 

191.  Section  of  Human  Epididymus, .    .  203 

192.  Section  of  Initial  Portion  of  Human  Vas  Deferens 204 

193.  Section  of  the  Cavernous  Portion  of  Human  Urethra, 205 

194.  Section  of  Ovary  of  Child 206 

195.  Section  of  Ovary  of  Infant, 207 

196.  Section  of  the  Cortex  of  Ovary  of  Rabbit, 207 

197.  Section  of  a  Large  Graafian  Follicle  of  Child .    .  208 

198.  An  Ovum  from  the  Graafian   Follicle  of  the  Cow, 208 

199.  Section  of  Uterus  of  a  Girl, • 211 

200.  Mucous  Membrane  of  the  Resting  Uterus  of  a  Voung  Woman, 212 


LIST    OF    ILLUSTRATIONS. 


201.  Mucous  Membrane  of  a  Virgin  Uterus  during  Menstruation •   .    .  213 

202.  Section  of  the  Mucous  Membrane  of  Human  Uterus,  One  Month  I'regnani,  ....  214 

203.  Section  of  the  Wall  of  a  Uterus,  Seven  Months  Pregnant, 215 

204.  Decidual  Cells  from  Human  Uterus,  Seven  Months  Pregnant, 216 

205.  Section  of  Normal  Human  Placenta  of  about  Seven  Months 218 

206.  Diagram  of  Human  Placenta  at  the  Close  of  Pregnancy,  219 

207.  Section  of  a  Smaller  and  a  Larger  Chorionic  Villus  of  Human  Placenta,    ...        .  220 

208.  Section  of  the  Skin  of  Finger  of  Adult  Man,  224 

209.  Section  of  the  .Skin  of  the  Sole  of  I'oot  of  Adult  Man 225 

210.  Dorsal  Half  of  a  Section  of  the  Third  I'halanx  of  Child, 226 

211.  Elements  of  Human  Nail •   .    .    .    .  227 

212.  Section  of  Human  Scalp, 228 

213.  Elements  of  Human  Hair  and  Hair  EoUicle 229 

214.  .Section  of  Human  Scalp 229 

215.  Section  of  the  Skin  of  Cheek  and  of  Forehead  of  Human  Emiiryo 230 

216.  Section  of  the  Hairy  .Scalp  of  Adult  Man, 231 

217.  .Section  of  the  Ala  Nasi  of  Child, 232 

218.  Section  of  the  Skin  of  the  Sole  of  Human  Foot 233 

219.  Section  of  Mammary  Gland  of  a  Pregnant  Rabbit 234 

220.  Section  of  Mammary  Gland  of  a  Woman, 235 

221.  Milk  Globules  of  Human  Milk,  Elements  of  the  Colosinun  of  a  Pregnant  Woman,  235 

222.  Section  of  Human  Cornea,     .        237 

223.  Section  of  Cornea  of  Ox, 238 

224.  Section  of  Cornea  of  Rabbit, 238 

225.  Section  of  a  Part  of  the  Human  Sclera  and  the  Entire  Choroid 238 

226.  Teased    Preparation    of   Human    Choroid;    Choriocapillaris  and  adherent    Hyaloid 

Membrane, 239 

227.  Section  of  the  Right  I rido  Corneal  Angle  of  Man, 240 

228.  Section  of  Pupillary  Portion  of  Human  Iris 240 

229.  Section  of  Human  Retina 242 

230.  .Section  of  Retina  of  Ral  bit, .  244 

231.  Scheme  of  the  Elements  of  the  Retina, 245 

232.  Isolated  Elements  of  Retina  of  Ape 246 

233.  Section  of  the  Macula  and  the  Center  of  the  Fovea  of  a  Man  .Sixty  Years  Old,  .    .    .  247 

234.  Section  of  Ora  Serrata  and  adjacent  Pars  Ciliaris  Retinse  of  a  Woman  Seventy-eight 

Years  tJld, 249 

235.  Section  of  Optic  Entrance  of  Human  Eye 250 

236.  Lens-Fibers  of  Infant 251 

237.  Capsule  and  Epithelium  of  Adult  Human  Lens, 251 

238.  Scheme  of  Vessels  of  the  Eye,  according  to  Leber, 254 

239.  Section  of  Human  Cornea, ....  256 

240.  Section  of  Upper  Eyelid  of  a  Six-Months'  Old  Child, 257 

241.  Section  of  Human  Lacrjmal  Gland, 259 

242.  Otoliths  from  the  .Sacculus  of  an  Infant 260 

243.  Section  of  the  Second  Turn  of  the  Cochlea  of  an  Infant 262 

244.  Surface  View  of  Lamina  Spiralis  of  Cat, 263 

245.  Surface  View  of  Lamina  Spiralis  Membranacea  of  Cat, 2(13 

246.  Lamina  Spiralis  of  Cat  seen  from  Vestibular  Surface, 264 

247.  Scheme  of  Structure  of  Tympanic  Wall  of  Duct  of  Cochlea, .  264 

248.  Surface  \'iew  of  Lamina  .Spiralis  Membranacea  of  Cat, 265 

249.  Section  of  Peripheral  Half  of  Osseous  and  of  Membranous  Spiral  lamina  of  Infant,  .  266 

250.  Section  of  Skin  of  External  .-Vuditory  Meatus  of  Infant 268 

251.  Sections  of  Coil    Tubule  of  External  Auditory  Meatu« 268 


XVI  LIST    OF    ILLUSTRATIONS. 

FIG.  PACK 

252.  Section  of  Respiratory  Mucous  Membrane  of  Uiiiiian  Nasal  Septum, 270 

253.  Isolated  Cells  of  Olfactory  Mucosa  of  Rabl:iit, 271 

254.  Section  of  Olfactory  Region  of  Young  Rabliit 271 

255.  Section  of  Olfactory  Mucosa  of  Rabbit,  X  5°.  ■    •    ■ ...  272 

256.  Section  of  Olfactory  Mucosa  of  Rabbit,  X  560, 272 

257.  Section  of  Two  Ridges  of  the  Papilla  Foliata  of  Rabbit 273 

258.  Section  of   Papilla  Foliata  of   Rabbit, 274 

259.  Section  of  Circumvallate  Papilla  of  Monkey, _ 274 

260.  Connective-Tissue  Cells  from  Corium  of  I'riton  Treniatus 276 

261.  Nerve-Fiber  of  Rabbit 281 

262.  Isolated  Elements  of   Fresh  Bone-Marrow 290 

263.  Section  of  Human  Cerebral  Cortex, 295 

264.  Transverse  Section  of   Spinal  Nerve  of  Rabbit, 296 

265.  Lower  Half  of  an  Isolated  Fundus  r.Iand 303 

266.  Intestinal  Villus   of   Rabbit, 304 

267.  Crypts   of   Lieberkiihn, 305 

268.  Isolated  Elements  of  Testicle, 312 


PART    I. 

GENERAL   TECHNIQUE. 
I.  THE    LABORATORY  APPOINTMENTS. 

I.   INSTRUMENTS. 

The  Microscope. — I  have  often  tested  the  excellent  workmanship  of 
the  microscopes  made  in  the  optical  workshops  of  Hartnack  in  Potsdam,  Leitz 
in  Wetzlar,  Seibert  in  Wetzlar,  and  Zeiss  in  Jena.* 

It  is  not  advi,sable  for  the  beginner  to  buy  a  microscope  without  previously 
placing  it  for  testing  in  the  hands  of  an  expert.  For  the  preservation  of  the 
raicro.scope  it  is  necessary  to  protect  it  from  dust.  When  in  constant  use,  it  is 
best  to  keep  it  under  a  bell-glass  in  a  place  not  exposed  to  sunlight.  Dirt 
should  be  removed  from  the  tube  with  a  dry  piece  of  soft  filter-paper ;  from 
the  lenses  and  mirror  with  soft  leather.  Balsam  may  be  removed  with  a  soft 
piece  of  linen  dampened  with  a  drop  of  alcohol.     Great  care  must  be  exercised 


*  I  advise  students  of  the  first  semestre  to  refrain  from  the  purchase  of  high-power  oculars 
and  immersion-systems.     These  should  not  be  bought  before  entrance  upon  bacteriological  work. 

The  following  are  reconmiended  : — 
Leitz.     Catalogue  No.  35,  1893.     Microsc. ,  No.  V.     Price  355  J/.  =$88.75.     (Without  liomog. 

Imniers.  and  without  Ocular  I\',  250  M.  :=S62.50. ) 
Seibert.     Catalogue  No.  22,,  1891,    Microsc,  4  a.    Price  498  i1/.  =  S129.00.    (Without  honiog. 

Immers.,  Objective  3,  and  Ocular  O,  272.5  M.  =  $68.15.) 
Zeiss.     Catalogue  No.  29,  189I,  page  120,  9)0.     Price  502  M.  =  S125.50.      (Without  homog. 

Immers.,  342  J/.  =585.50.)     Or  lo)c.      Price  485  y)/.     (Without  homog.  Immers.,  324 

M.  =S8i.oo.) 

In  the  preparation  of  this  book  I  have  carried  on  the  majority  of  the  investigations  with  a 
microscope  of  Leit/. 

Editor  s  Remark. — In  the  U.  S.  A.  a  duty  of  35  per  cent,  in  addition  to  the  above  prices 
of  foreign  microscopes  must  be  paid. 

Of  American  microscopes  those  from  the  manufactory  of  Baiisi/i  i&^  Lomb  Optical  Co. , 
Rochester,  N.   V. ,  attii  A'ew  Yori  City,  may  be  recommended. 

For  ordinary  histological  work  the  following  is  suitable  : — 
Stand  li.  B. — Ocular  I  X  3-     Objectives  \  inch  an<l  \  inch.     (Catalogue,  1895.)     Price  S62.50. 

Kor  cytological  and  bacteriological  work  a  ^j  inch  of  oil  immersion  (price  $44.00)  and  an 

Aibl  condenser  with  iris  diaphragm  should  be  added. 
For  convenience  a  double  or  triple  rerolver  for  objectives  is  desirable. 
2  17 


iS  HISTOLOCV. 

in  the  last  case,  lest  the  alcohol  penetrate  and  loosen  the  balsam-setting  of  the 
lens.  The  lens  should,  therefore,  be  quickly  washed  and  carefully  dried.  The 
screws  of  the  microscope  may  be  cleaned  with  benzine. 

A  good  razor,  flat  on  one  side.  It  should  always  be  kept  sharp.  The 
honing  of  it  should  be  left  to  the  instrument  maker;  but  before  using  it  each 
time  it  should  be  drawn  without  pressure  over  the  strop.  This  razor  ought  to 
be  used  only  in  the  preparation  of  thin  sections. 

A  fine  oil-stone. 

A  fine  pair  of  straight  scissors. 

A  pair  of  easily  closing  fine  forceps,  with  smooth  or  only  slightly  notched 
points. 

Four  teasing  needles  with  wooden  handles,  two  of  which  may  be  heated, 
then  slightly  bent,  heated  once  more,  and  stuck  into  solid  paraffin,  whereby 
they  are  again  hardened.  The  other  two  must  be  kept  clean  and  highly  pol- 
ished, as  for  the  work  of  teasing  the  needles  must  be  sharply  pointed.  They 
may  be  first  sharpened  on  the  stone  and  then  polished  on  the  strop.  The  so- 
called  cataract-knives  of  the  oculists  are  very  useful. 

A  section- lifter  {spatula),  to  transfer  sections  from  fluids  to  the  slide,  is 
useful  but  not  absolutely  necessary.  The  broad  blade  of  a  dissecting  knife 
can  be  substituted. 

Pins,  quills,  cork  discs,  a  fine  faint-iirusli. 

A  crayon  for  writing  on  glass.* 

Slides  should  be  of  clear  glass  and  not  too  thick  (i  to  1.5  mm.). 

Cover-glasses  measuring  15  mm.  in  diameter  are  generally  large  enough. 
Their  thickness  may  vary  from  o.i  to  0.2  mm. 

Small  ^/(Zj-j-  bottles  (the  so-called  powder-bottles),  one  dozen,  with  broad 
neck  and  a  capacity  of  30  and  more  c.c.  Bottles  with  glass  stoppers  are  too 
expensive  and  not  desirable,  as  the  stoppers  are  often  poorly  ground. 

Some  small  glass  jars  with  ground  covers  about  8  to  10  cm.  high  and 
6  to  10  cm.  in  diameter. 

A  cylindrical g7'aduate,  capacity  100  to  150  c.c. 

A  glass  funnel,  upper  diameter  8  to  10  cm. 

A  pipette.  Small  pipettes  may  be  prepared  by  heating  in  a  gas-flame  a 
glass  tube  i  cm.  thick  and  10  cm.  long,  pulling  one  end  to  a  point,  and 
placing  on  the  other  a  small  rubber  bulb. 

A  dozen  watch-glasses  of  5  cm.  diameter. 

A  dozen  test  tubes  lo  cm.  long  and  12  mm.  wide. 

Glass  rods  3  mm.  thick,  15  cm.  long,  some  drawn  to  a  point  at  the  end. 

Old  medicine  glasses  and  bottles,  which  have  been  thoroughly  cleansed, 
serve  as  receptacles  for  reagents,  f 


*  If  the  glass  is  oily  it  must  first  be  cleansed  with  alcohol. 

f  In  most  cases  the  bottles  may  be  sufficiently  cleansed  with  water,  but  sometimes  it  will 
be  necessary  to  clean  them  with  crude  muriatic  acid,  or  caustic  lye,  then  with  ordinary  water, 
next  with  distilled  water,  and  finally  with  alcohol. 


THE    LABORATORY    APPOINT.MKM  S. 


19 


Glass  dislu-s,  10  to  12  cm.  diameter,  with  ground  covers,  are  not  absolutely 
necessary,  but  very  useful.* 

In  many  ca-ses  these  may  be  replaced  by  saucers,  food  dishes  for  birds,  etc. 

A  few  sheets  of  thin,  yi\\\\.t  filter-paper,  large  and  small  gummed  labels,  soft 
pieces  of  linen  (old  handkerchiefs),  a  towel,  a  large  and  a  small  bottle-brush. 

A  large  stone  jar  for  refuse. 

2.  REAGENTS.f 
General  Rules. — Large  quantities  should  not  be  kept  on  hand,  for  many 
reagents  decompose  in  a  comparatively  short  time.  Some  should  be  prepared 
just  before  they  are  to  be  used  {ef.  following).  Each  bottle  must  have  its 
contents  designated  by  a  large  label.  It  is  advisable  to  place  on  the  label  not 
only  the  formula  of  the  fluid  referred  to,  but  also  the  manner  of  its  application. 
The  several  bottles  must  be  closed  tightly  with  cork  or  good  glass  stoppers. 
The  fluid  should  not  reach  the  lower  surface  of  the  cork. 

1.  Distilled  water  3  to  6  liters. 

2.  Normal  salt  solution  0.75  per  cent.,  aq.  destill.  200  c.c,  salt  1.5  gm. 
The  cork  must  be  provided  with  a  glass  rod  reaching  to  the  bottom  of  the 
bottle.     This  reagent  spoils  easily  andhwust  often  be  renewed. 

3.  Akohol. — (<?)  Absolute  alcohol,  in  quantity  of  about  200  c.c.  The 
absolute  alcohol  of  commerce  is  95  per  cent.,  and  answers  for  most  microscopi- 
cal purposes.  If  it  is  desired  to  obtain  alcohol  free  from  water,  drop  into  the 
bottle  a  {^\s  pieces  of  copper  sulphate  heated  to  white  heat  (15  gm.  to  100  c.c. 
alcohol).  If  these  become  blue  they  must  be  replaced  by  new  pieces,  or  be 
reheatec^.     Fresh  quicklime  serves  the  same  purpose,  but  acts  more  slowly. 

{U)  Ninety  per  cent.  Alcohol. — Five  hundred  c.c.  are  prepared  by  diluting 
475  c.c.  95  per  cent,  alcohol  with  25  c.c.  distilled  water.]; 

(c)  Sei'enty  per  cent.  Alcohol. — Five  hundred  c.c.  are  prepared  by  dilut- 
ing 370  c.c.  95  per  cent,  alcohol  with  130  c.c.  distilled  water. 

((/)  Ranvier  s  J3  per  cent.  Alcohol. — Thirty-five  c.c.  95  percent,  alcohol 
and  65  c.  c.  distilled  water. 


*  Most  of  the  above-mentioned  glassware  (including  slides)  may  be  obtained  cheaply  of 
W.  P.  Slender,  Leipzig  [Dam/fglasiclileiJ'erei),  and  Dr.  Bender  and  Dr.  Hobein  in  Miouhen 
( Gabtlsbergerstr. ) . 

■f  The  reagents  must  be  obtained  from  a  reliable  chemist  or  well-known  drug-house.  Ex- 
cellent stains  and  reagents  are  obtainable  from  Dr.  Griibter,  Physiologieal  Laboratory,  Leipzig, 
Bayei'iche  Strasse  6j. 

X  To  obtain  the  desired  ptr  cent,  of  alcoholic  mixtures,  this  ratio  will  serve  : — 
100  :  95  =  X  :  '/t . 
e.  g.,  90^; ,  100  :  95  =  X  :  90 
95  X  =  90.  100 
0000 
^=  -^5     =94.7  or  95 

Therefore,  to  obtain  lOO  c.c.  90  per  cent,  alcohol,  95  c.c.  of  95  per  cent,  alcohol  must  be  mixed 
with  5  c.c.  distilled  water,  l-'or  our  purposes  the  mistakes  of  this  ratio  are  too  insignificant  for 
consideration . 


20  HISTOLOGY. 

4.  Aci-tic  AciJ,  50  c.c. — The  official  is  30  per  cent. 

5.  Glacial  acetic  a^/(/ should  be  procured  shortly  before  using  (10  c.c). 
That  obtainable  from  the  chemist  is  96  per  cent. 

6.  Nitric  Acid. — A.  bottle  should  be  kept  on  hand  with  100  c.c.  concen- 
trated nitric  acid  of  1.18  sp.  gr.  (containing  32  per  cent,  acid  hydrate). 

7.  Pure  hydrochloric  acid,  50  c.c. 

8.  Chromic  Acid. — -A  10  per  cent,  stock  solution  should  be  prepared  (10 
gm.  of  recently  prepared  crystallized  chromic  acid  dissolved  in  90  c.c.  distilled 
water).  From  this  can  be  made  (a)  a  o.i  per  cent,  chromic  acid  solution 
(10  c.c.  of  stock  solution  to  990  c.c.  distilled  water),  and  (li)  a  0.5  per  cent, 
chromic  acid  solution  (50  c.c.  of  stock  solution  to  950  c.c.  distilled  water). 

9.  Potassium  bichromate  should  be  kept  on  hand  in  the  following  prepara- 
tions :  (a)  25  gm.  in  1000  c.c.  distilled  water;  {b)  35  gm.  in  1000  c.c. 
distilled  water,  for  the  Golgi  mi.xture  (No.  11).  This  dissolves  slowly  in  three 
to  six  days  at  room  temperature.  Make  the  solution,  therefore,  with  warm 
water,  or  place  the  bottle  near  the  stove. 

10.  Milller' s  Fluid. — Thirty  gm.  sodium  sulphate  and  60  gm.  pulverized 
potassium  bichromate  are  dissolved  in  3000  c.c.  distilled  water.  Solution 
can  be  aided  by  heat,  as  in  9. 

11.  Goli^i's  mixture'-^  (osmio-bichromate  mi.xture),  to  be  obtained  by 
pouring  together  54  c.c.  of  the  3.5  per  cent,  solution  of  bichromate  of  potash 
(9^)  and  6  c.c.  of  the  2  per  cent,  osmic-acid  solution  (i8).  To  be  prepared 
shortly  before  using.    In  the  application  of  the  Golgi  method  we  need  further — 

12.  A  solution  of  silver  7titrate,  0.75  per  cent.,  which  is  prepared  by  mix- 
ing 150  c.c.  of  I  per  cent,  solution  (22)  with  50  c.c.  distilled  water  and  a 
drop  of  formic  acid.      To  be  made  shortly  before  using. f 

For  "fixing"  the  Golgi  preparations  we  need — 

13.  Hydrochinous  developer,  5  gm.  hydrochinon,  40  gm.  sodium  sulphate, 
75  gm.  calcium  carbonate,  250  gm.  aq.  destill.  From  this  a  dilution  may  be 
made  by  mixing  20  c.c.  of  the  mixture  and  230  c.c.  of  the  aq.  destill.  In 
a  dark  place,  in  a  well-closed  bottle,  it  keeps  strong  for  weeks.  The  yellow 
color,  which  appears  with  time,  does  not  interfere  with  its  action. 

14.  Sodium  Hyposulphite  (10  gm.  in  50  c.c.  distilled  water). — It  dissolves 
quickly  without  heating. 

15.  Picric  Acid. — One  should  keep  on  hand  50  gm.  of  the  crystals  and 
500  c.c.  of  a  saturated,  aqueous  solution,  in  which  a  certain  amount  of  undis- 
solved crystals  must  always  be  present  on  the  bottom  of  the  bottle.  It  dissolves 
easily. 

16.  Picro-sulphuric  Acid,  Kleinenberg  s  Solution. — -To   200  c.c.  of  satu- 


*  Editor' s  Remark.  —  Co.x-Golgi  mixture  is  obtained  by  pouring  together  40  c.c.  of  5  per 
cent,  solution  of  bichromate  of  potash,  40  c.c.  of  5  per  cent,  solution  of  corrosive  sublimate, 
32  c.c.  of  5  per  cent,  solution  of  chromate  of  potash  and  88  c.c.  distilled  water.  This  mix- 
ture may  be  kept  a  long  time  in  stock. 

■f  Old  silver  solution  of  0.75  per  cent,  not  acidulated  is  equally  useful. 


■IHR    I.AIiOKAlOKV    APPOINTMENTS.  2  1 

rated  aqueous  solution  of  picric  acid  are  added  4  c.c.  of  pure  sulphuric  acid. 
A  strong  precipitate  forms.  After  an  hour  the  mixture  is  filtered  and  diluted 
with  600  c.c.  of  distilled  water. 

17.  Chroino-acetic  Acid. — To  50  c.c.  0.5  per  cent,  chromic  acid  solu- 
tion (8  b)  are  added  50  c.c.  distilled  water  and  3  to  5  drops  glacial  acetic  acid. 

18.  Osmic  acid,  50  c.c.  of  2  per  cent,  aqueous  solution  may  be  obtained 
from  the  chemist.  (Very  expensive))  It  is  to  be  kept  in  the  dark  or  in  a 
dark  bottle,  and  when  well  closed  will  remain  strong  many  months. 

19.  Chromo-aceto-osmic  Acid  {J^kmming' s  Solution). — Prepare  a  i  per 
cent,  chromic  acid  solution  (5  c.c.  of  the  10  per  cent,  solution  (8)  to  45  c.c. 
distilled  water).  Add  12  c.c.  of  2  per  cent,  osmic  acid  and  3  c.c.  glacial 
acetic  acid.  This  mixture  is  not  injured  by  light  and  can  be  long  kept  in 
stock.* 

20.  Chloride  of  Platinum  (expensive!). — Keep  a  10  per  cent,  stock  solu- 
tion, 2  gm.  dissolved  in  20  c.c.  distilled  water. 

21.  Pliitino-aceto-osmic  Mixture  (^Hermann' s  Solution). — Pour  into  60 
c.c.  of  I  per  cent,  solution  of  chloride  of  platin  (6  c.c.  of  stock  solution  and 
54  c.c.  distilled  water),  8  c.c.  2  per  cent,  osmic  solution  and  4  c.c.  glacial 
acetic  acid. 

22.  Silver  Nitrate. — Obtain  from  the  chemist,  a  short  time  before  using,  a 
solution  of  I  gm.  argent,  nitric,  in  100  c.c.  distilled  water.  To  be  kept  in 
the  dark  or  in  a  dark  bottle. 

23.  Chloride  of  Gold. — Obtain  from  the  chemist,  a  short  time  before 
using,  a  solution  of  i  gm.  chloride  of  gold  in  100  c.c.  distilled  water.  To  be 
kept  in  the  dark  or  in  a  dark  bottle.      For  gold-staining  we  need  further  — 

24.  Formic  acid,  50  c.c. 

25.  Saturated  Potash  Lye  (35  per  cent.)  30  c.c. — The  bottle  must  be 
closed  with  a  rubber  stopper  provided  with  a  glass  rod.  Obtained  at  the 
chemist's. 

26.  Glycerine. — One  hundred  c.c.  of  pure  glycerine  is  to  be  kept  in  stock 
and  also  a  dilution  of  5  c.c.  of  pure  glycerine  in  25  c.c.  distilled  water.  To 
prevent  the  appearance  of  fimgi  in  this  mixture,  add  5  to  10  drops  pure  i  jjer 
cent,  carbolic,  acid  solution  or  a  chloral  hydrate  crystal.  The  cork  of  the 
bottle  should  be  provided  with  a  glass  rod. 

27.  Bergamot  Oil  (green),  20  c.c. — The  oil  of  cloves,  which  is  cheaper 
and  hence  frequently  used,  scents  the  whole  laboratory.  The  bottle  should  be 
provided  as  above. 

(a)  Xylol  to  replace  bergamot  oil  in  special  cases.  Xylol  clears  up  more 
strongly  and  is  not  to  be  recommended  to  beginners  because  of  its  sensitive- 
ness in  preparations  incompletely  freed  from  water. 

28.  Damar-varnish  of  Dr.  Fr.  Schonfeld  &  Co.,  of  Diis-seldorf,  is  pur- 
chasable in  small   bottles  of  50  c.c.  in  art  stores.      If  it  is  too  thick  it  may  be 


*  Tissues  fixed  will)  old  Flemraing's  fluid  often  stain  badly  because  the  acetic  acid  has 
evaporated  ;  5  to  20  drops  of  actrtic  acid  newly  added  to  the  sohition  removes  this  delect. 


2  2  HISTOLOGY. 

diluted  with  pure  turpentine.  It  has  the  proper  consistency  if  the  drops, 
from  an  inserted  glass  rod,  fall  without  drawing  long  threads.  Damar  is  prefer- 
able to  Canada  balsam  (diluted  with  chloroform),  which  renders  the  specimens 
too  transparent.  But  it  has  the  disadvantage  of  drying  very  slowly,  while  balsam 
dries  quickly.     The  cork  of  the  bottle  must  be  furnished  with  a  glass  rod. 

((7)  Xy/o/-ba/sam,  solution  of  Canada  balsam,  a  substitute  for  damar- 
varnish. 

29.  Ci)VtT-g/ass  Cement. — Venetian  turpentine  is  diluted  with  ether  suffi- 
cient to  make  the  solution  drop  easily.  It  is  then  filtered  warm  (through  a 
heated  funnel)  and  the  liquid  inspissated  on  a  sand  bath.  The  proper  con- 
sistency is  reached  when  a  drop  transferred  with  a  glass  rod  to  a  slide  hardens 
at  once  and  can  be  no  longer  indented  with  the  finger-nail.  It  is  better  to 
have  the  cement  prepared  by  the  chemist  because  of  the  danger  of  fire. 

30.  Bohmer' s  Hatnafoxylin. — (a)  One  gm.  of  hsematoxylin  crystals  is  dis- 
solved in  10  CO.  absolute  alcohol.  (/')  Twenty  gm.  alum  are  dissolved  in  200 
c.c.  warm  distilled  water  and  filtered  after  cooling.  The  two  solutions  are 
poured  together  the  next  day  and  remain  standing  a  week  in  an  open  vessel. 
After  the  mixture  is  filtered  it  is  ready  for  use.  Cloudiness  or  growth  of  fungi 
in  the  fluid  do  not  interfere  with  its  action  in  the  slightest  degree.  To  be  kept 
in  stock.      Instead  of  Bohmer's  haematoxylin — 

31.  Hamahim  may  be  used.  One  gm.  hEematin-ammonium  *  is  dissolved 
by  the  application  of  heat  in  50  c.c.  of  95  per  cent,  alcohol  and  added  to  a 
solution  of  50  gm.  alum  in  i  liter  distilled  water.  To  this  add  some  drops  of 
thymol.      The  mixture  can  be  used  at  once  and  keeps  well. 

32.  DelafiehV s  Hamatoxylin. — (a)  One  gm  crystallized  haematoxylin  is 
dissolved  in  6  c.c.  absolute  alcohol.  (/;)  Fifteen  gm.  ammonium-alum  are  dis- 
solved in  100  c.c.  distilled  water,  and  after  cooling,  filtered.  The  two  solu- 
tions are  then  ])oured  together,  and  the  mixture  left  standing  three  days  in 
an  open  vessel  in  the  light.  It  is  then  filtered  and  mixed  with  25  c.c.  pure 
glycerine  and  25  c.c.  methyl-alcohol.  After  three  days  the  mixture  is  filtered 
and  may  be  kept  a  long  time  in  stock. 

T,2,.  Weigert' s  hamatoxylin  for  demonstration  of  the  medullated  nerve- 
fibres  of  brain  and  spinal  cord.  One  gm.  hsematoxylin  is  placed  in  10  c.c. 
absolute  alcohol  +  90  c.c.  distilled  water,  heated,  and,  after  cooling,  filtered. 
To  be  made  ready  shortly  before  using.  The  application  of  this  stain  demands 
the  aid  of  a — 

34.  Saturated  Solution  of  Lithium  Carbonate. — Three  to  4  gm.  lith.  carb. 
dissolved  in  100  c.c.  distilled  water.     To  keep  in  stock.     Further — 

35.  A  0.2^  per  cent.  Solution  Permanganate  0/  Potash. — Five  gm.  per- 
manganate of  potash  to  200  c.c.  distilled  water.      Prepared  a  day  before  using. 

36.  Acid  Mixture  (Pal's  Mixture). — One  gm.  acid  oxal.  pur.  and  i  gm. 
potassium  sulphite  (SO^K.^)  dissolved  in  200  c.c.  distilled  water.  This  mix- 
ture is  prepared  a  day  before  using  and  is  kept  in  a  well-closed  bottle. 

*  To  be  obtained  of  Dr.  Griibler,  Leipzig. 


THE    LABORATURV    APPOINTMENTS.  23 

37.  Neutral  Carmine-solution. — One  gm.  of  the  best  carmine  is  dissols'ed, 
cold,  in  50  c.c.  distilled  water  with  an  addition  of  5  c.c.  liq.  ammon.  caust. 
The  deep  cherry-red  fluid  should  be  kept  in  an  open  vessel  till  it  has  no  odor 
of  ammonia  (about  three  days),  and  then  be  filtered.  To  keep  in  stock. 
The  odor  of  this  solution  immediately  becomes  very  disagreeable  but  does  not 
interfere  with  the  staining  power  of  the  fluid. 

38.  Picro-carmine. — Add  to  a  mixture  of  50  c.c.  distilled  water  and  5 
c.c.  liq.  ammon.  caust.  i  gm.  best  carmine.  Stir  with  glass  rod.  After  com- 
plete solution  of  the  carmine  (about  five  minutes),  add  50  c.c.  saturated  picric 
acid  solution,  and  leave  the  whole  standing  two  daj's  in  an  ojien  vessel.  Then 
filter.  Abundant  fungous  growth  does  not  diminish  the  staining  power  of  this 
excellent  medium. 

39.  Alum-carmine. — Five  gm.  alum  are  dissolved  in  100  c.c.  warm,  dis- 
tilled water  and  then  2  gm.  carmine  added.  This  mixture  is  heated  from  ten 
to  twenty  minutes,  and,  after  cooling,  filtered.  Finally  to  the  clear  ruby-red 
fluid  2  to  3  drops  acid,  carbol.  liquefact.  are  added. 

40.  Bora.x-carmine. — Dissolve  4  gm.  borax  in  100  c.c.  warm,  distilled 
water,  and,  after  cooling,  add  3  gm.  carmine,  stirring  meanwhile.  Then  pour 
in  this  mixture  100  c.c.  70  per  cent,  alcohol.  After  twenty-four  hours,  filter 
the  fluid. 

Staining  with  borax-carmine  requires  after-treatment  with  70  per  cent, 
acid-alcohol,  which  is  prepared  by  adding  4  to  6  drops  of  pure  hydrochloric 
acid  to  100  c.c.  70  per  cent.  (3  <■)  alcohol.     Both  to  be  kept  in  stock. 

41.  Sodium  Carminate. — Two  gm.  of  stain  dissolved  in  200  c.c.  distilled 
water. 

42.  Saffranin. — Two  gm.  of  the  stain  dissolved  in  60  c.c.  50  per  cent, 
alcohol  (31  c.c.  96  per  cent,  alcohol  -\-  29  c.c.  distilled  water).  To  be  kept 
in  stock. 

43.  Eosin. — One  gm.  stain  dissolved  in  60  c.c.  50  per  cent,  alcohol.  To 
be  kept  in  stock. 

44.  Congo  Red. — One  gm.  color  dissolved  in  100  c.c.  distilled  water. 
From  this  stock-solution  is  prepared — 

(a)  A  .j'jy  per  cent,  solution:  3  c.c.  stock-solution  to  100  c.c.  distilled 
water. 

45.  Vesuvin  (^Bismarck  brown)  or — 

46.  Methylviolet  B  can  be  kept  in  stock  in  a  saturated  aqueous  solution 
(i  gm.  to  50  c.c.  distilled  water). 

47.  Methylene  Blue. — One  gm.  dissolved  in  100  c.c.  distilled  water. 

48.  Ammonium  Picrate. — Three  gm.  to  100  c.c.  distilled  water.  This 
keeps  a  long  time. 

49..  W'estphaV s  Alum-carmine  Dahlia. — Dissolve  i  gm.  dahlia  in  25  c.c. 
absolute  alcohol.  Add  12  c.c.  pure  glycerine  and  5  c.c.  glacial  acetic  acid 
and  pour  into  this  mixture  25  c.c.  alum-carmine  (39).  To  be  kept  in  well- 
closed  bottles. 


II.   THE  PREPARATION  OF  MICROSCOPICAL 
SPECIMENS. 

INTRODUCTION. 

Very  few  organs  of  the  animal  body  are  of  a  structure  "suitable  for  micro- 
scopical examination  without  special  jireparation.  They  must  possess  a  certain 
degree  of  transparency  which  is  attained  either  by  separating  the  organs  into 
their  elements,  ?'.  c,  isolating  the  latter,  or  by  cutting  the  organs  into  thin 
sections.  On  the  other  hand  there  are  very  few  tissues  which  allow  of  cutting 
into  very  thin  sections.  They  are  either  too  soft,  in  which  case  they  must  be 
liardened,  or  too  hard  (calcified),  in  which  case  they  must  be  decalcified.  Fresh 
tissues,  however,  cannot  immediately  be  harde?ied  or  deca/cified  withont  injury 
to  their  structure.  Accordingly  both  processes  must  be  preceded  by  a  treat- 
ment which  kills  the  structural  elements  rapidly  and  at  the  same  time  preserves 
their  natural  form.  This  procedure  is  called  fixation.  The  preparation  of 
fine  sections,  therefore,  is  possible  only  after  the  processes  of  fixing  and  hard- 
ening.* The  sections,  moreover,  require  still  further  treatment.  They  may 
first  be  made  transparent  by  a  clearing  agent  immediately  after  cutting  (a  pro- 
cess which  is  also  successfully  employed  with  tissues  examined  in  a  fresh 
condition),  or  they  may  be  stained  before  being  made  transparent.  Staining 
materials  are  invaluable  helps  in  microscopical  examinations.  They  can  be 
applied  to  fresh  and  even  to  living  organs.  Many  very  important  facts  have 
been  discovered  by  their  aid.  Injected  into  the  blood-vessels  they  make  evident 
their  distribution  and  the  course  of  their  finest  branches. 

§  I.   NATURE  OF  THE  MATERIAL. 

For  the  study  of  the  histological  elements  and  the  simplest  tissues,  amphi- 
bians (frogs,  salamanders)  are  recommended.  The  best  is  the  spotted  sala- 
mander {Salamandra  maculosa),  f  whose  elements  are  very  large.  For  the  ex- 
amination of  the  organs  mammals  may  be  chosen.  Our  rodents  (rabbits, 
guinea-pigs,  rats,  mice,  or  young  dogs,  cats,  etc.)  suffice  for  many  purposes. 
Still  no  opportunity  to  procure  the  organs  of  man  should  be  neglected.  En- 
tirely fresh  material  can  often  be  obtained  from  the  surgical  clinics. 

In  general  it  is  advisable  to  place  the  organs  in  the  fixing  fluid  while  they 
are  yet  warm.     To  accomplish  this  it  is  recommended  to  first  fill  the  bottles 

*  (Followed,  if  necessary,  by  decalcification). 

f  Editor's  Remark. — Or  the  American  A mli/ystoma ,  A'ictiinis,e\c. 

24 


THE    PREPARATION    OF    MICROSCOPICAL    SPECIMENS.  25 

chosen  for  the  reception  of  the  tissues,  then  to  provide  them  with  labels  upon 
which  is  designated  the  object,  the  fluid  used,  and  the  date — even  the  hour. 
The  instruments  necessary  for  dissecting  should  be  placed  in  order  near  at 
hand.     Now  the  animal  may  be  killed.* 

§2.   KII.LLW;  Am)  DISSECTING  THE  .WI.M.VLS. 

In  the  case  of  amphibians,  cut  with  strong  scissors  through  the  vertebral 
column  of  the  neck,f  and  destroy  brain  and  spinal  cord  by  means  of  a  needle 
introduced  into  the  spinal  canal  and  cranial  cavity.  In  the  case  of  mammals, 
cut  the  throat  of  the  animal  by  a  deep  incision  reaching  as  far  back  as  the 
vertebral  column  of  the  neck,  or  kill  it  by  pouring  chloroform  on  a  cloth  and 
pressing  it  to  the  nose  of  the  animal.  Embryos,  small  animals  to  the  size  of 
4  cm.,  may  be  thrown  entire  into  the  fixing  fluid.  After  about  two  hours  the 
abdomen  and  thorax  may  be  opened  by  means  of  fine  scissors.  In  the  dissec- 
tion, whenever  possible,  an  assistant  should  hold  the  e.xtremities  of  the  animal. 
Small  animals  can  be  stretched  on  cork-  or  wax-plates,  fastening  them  by 
strong  pins  through  the  feet.  The  organs  must  be  taken  out  carefully.  This 
is  best  done  with  scissors  and  forceps.  Crushing  or  pressing  the  parts,  or  taking 
hold  of  them  with  the  fingers,  is  to  be  entirely  avoided.  Onfy  the  edge  of  the 
object  should  be  grasped  by  the  forceps,  .\ttached  mucus,  blood,  contents 
of  the  intestines,  etc.,  should  not  be  scraped  off"  with  a  scalpel,  but  may  be 
removed  by  slowly  twirling  them  in  the  respective  fixing  fluids. 

In  the  following  manipulations  it  is  inevitable  to  bring  the  scissors,  for- 
ceps, needles,  glass-rods,  etc.,  in  contact  with  the  different  fluids,  e.  g.,  acids. 
The  instruments  should  therefore  be  cleaned  immediately  after  using  by  rinsing 
them  in  water  and  drying  them,  .^bove  all,  avoid  dipping  a  glass-rod  which 
may  be  contaminated,  for  instance,  with  acid  or  dye,  into  another  fluid.  It  is 
obvious  that  the  reagents  would  thereby  be  spoiled.  The  success  of  the  prepa- 
ration is  often  entirely  fnistrated  by  such  inaccuracy.  The  jars,  watch-glasses, 
etc.,  are  easy  to  clean  if  attended  to  directly  after  using.  If.  however,  there  is 
not  time  for  this,  the  watch-glasses  should  be  at  least  thrown  into  a  dish  of 
water. 

.\11  vessels  used  for  isolating,  fixing,  hardening,  or  staining  must  be  kept 
closed.  (.\  watch-glass  is  covered  with  a  second  one,  if  the  work  with  it 
extends  beyond  ten  minutes.)     They  should  not  be  placed  in  the  sun. 

S  3.   ISOLATING. 
The  process  of  isolation  is  accomplished  by  teasing  either  the  fresh  tissues 
or  those  previously  treated  with  macerating  fluids.     In  the  latter  case  the  isola- 
tion has  been  entirely  or  in  part  accomplished  by  action  of  the  fluid.     It  is  a 
difficult  task  to  make  a  well-tea.sed  preparation.     Great  patience  and  e.xact 

*  To  take  parts  from  the  living  animal  is  an  entirely  needless  cruelty  ! 
t  In  doing  this,  hold  the  frog's  hind  legs  with  a  cloth  in  the  left  hand. 


2  0  HISTOLOGY. 

obedience  to  the  following  directions  will  be  indispensable.  The  needles  must 
be  sharp  and  perfectly  clean.  They  should  previously  be  pointed  on  a  moist- 
ened whet-stone.  The  stiiall  piece  of  tissue,  at  the  most  5  mm.  on  a  side,  is 
now  placed  in  a  small  drop  on  a  slide  and  teased  on  a  dark  background  if  it 
is  colorless,  on  a  white  surface  if  it  is  dark  (or  colored).  If  the  tissue  is 
fibrous,  e.  g.,  a  muscle-fibre  bundle,  both  needles  are  first  applied  to  one  end, 
and  the  bundle  broken  in  two,  lengthwise,  by  gradually  separating  the  points.* 

In  the  same  manner  one  of  these  half-bundles  is  again  divided,  and  so  on 
until  fine  single  fibres  have  been  isolated.  By  examination  of  the  uncovered 
preparation  with  low  power  we  may  ascertain  whether  the  necessary  degree  of 
isolation  has  been  attained,  f 

As  isolating  fluids  the  following  are  to  be  recommended  : — 

(a)  For  Epithelium. — Ranvier's  33  per  cent,  alcohol  (p.  19),  an  ex- 
cellent medium  for  isolation.  Lay  small  pieces  from  5  to  10  mm.  on  a  side, 
e.  g.,  intestinal  mucous  membranes,  into  about  10  c.c.  of  this  fluid.  After 
four  hours  (in  the  case  of  stratified  pavement  epithelium,  after  ten  to  twenty- 
four  hours  or  later)  the  pieces  are  taken  out  slowly  and  carefully  with  the  for- 
ceps, and  struck  lightly  a  few  times  upon  the  slide  in  a  drop  of  the  same  fluid. 
.\s  a  result  of  this  striking  many  cells  drop  off"  either  isolated  or  in  shreds, 
which  latter  may  be  broken  up  by  stirring  the  fluid  slightly  with  the  needle. 
Now  apply  a  cover-glass  (p.  38)  and  examine.  If  staining  of  the  specimen  is 
desired,  the  entire  piece  must  be  carefully  transferred  from  the  alcohol  into 
about  6  c.c.  picro-carmine  (p.  23).  After  two  to  four  hours  the  piece  is 
placed  very  carefully  in  5  c.c.  distilled  water,  and  after  five  minutes  struck 
upon  the  slide,  this  time  in  a  drop  of  dilute  glycerine  (p.  21).  Apply  a 
cover-glass.     The  preparation  can  be  preserved. 

{b)  For  Muscle  Fibres,  Glands. — Thirty-five  per  cent,  potash  lye  is  suit- 
able (p.  21).  Pieces  from  10  to  20  mm.  a  side  may  be  laid  into  10  to  20  c.c. 
of  this  fluid.  After  about  an  hour  the  pieces  fall  into  their  elements.  These 
may  then  be  lifted  out  with  a  needle  or  a  pipette,  and  examined  under  a  cover- 
glass  in  a  drop  of  the  same  lye.  Diluted  potash  lye  works  quite  differently,  as 
in  this  medium  the  elements  are  destroyed  in  a  short  time.  If  the  isolation  is 
not  successful,  but  instead  a  pappy  softening  occurs,  the  lye  is  too  old,  and  a 
fresh  solution  should  be  made.  The  preparations,  even  when  successful,  can- 
not be  preserved. 

A  mixture  of  potassium  chlorate  and  nitric  acid  may  be  used.  Prepare 
this  by  throwing  into  20  c.c.  of  pure  nitric  acid  (p.  20)  about  5  gm.  of  potas- 
sium chlorate,  which  will  be  sufficient  to  allow  an  undissolved  portion  to  re- 
main at  the  bottom.     After  one  to  six  hours,  often  longer,  the  specimen  is 

*  At  times  it  is  difficult  to  divide  the  bundle  along  its  entire  length.  In  this  case,  it  is 
often  sufficient  to  break  up  only  '^  of  its  length,  so  that  the  isolated  fibres  still  hang  all  together 
at  the  other  end. 

t  Specimens  lying  in  a  small  amount  of  fluid  and  not  covered  with  a  cover  glass  appear 
often  indistinct,  show  black  outlines,  etc.  By  the  addition  of  more  fluid  and  the  use  of  a  cover- 
glass  these  conditions  are  removed. 


THE    PREPARATION    OF    MICROSCOPICAL    SPECIMENS.  2  J 

sufficiently  macerated,  and  is  then  immersed  in  20  c.c.  distilled  water. 
Here  it  should  remain  an  hour,  but  may  stay  a  week  without  decomposing. 
Then  it  is  transferred  to  the  slide,  on  which,  in  a  drop  of  dilute  glycerine,  it 
can  be  easily  teased.  When  the  nitric  acid  is  well  washed  out,  the  prepara- 
tion maybe  stained  under  the  cover-glass  (p.  41),  and  preserved.  Placing 
the  unteased  pieces  in  picro-carmine  (see  the  isolation  of  epithelium)  will  not 
be  successful,  because  this  staining  fluid  renders  the  objects  brittle. 

((•)  For  gland-tubules,  place  the  small  pieces,  i  cm.  a  side,  in  10  c.c.  of 
pure  hydrochloric  acid.  After  ten  to  twenty  hours  they  are  transferred  into 
30  c.c.  distilled  water,  which  must  be  changed  several  times  within  twenty- 
four  hours.  It  is  then  an  easy  matter  to  bring  about  the  isolation  by  carefully 
spreading  the  small  pieces  with  a  needle  in  a  drop  of  dilute  glycerine.  The 
specimens  may  be  preserved. 

S  4-  FIXATION. 
General  Rules. —  i.  For  fixing,  the  quantity  of  the  fluid  used  should 
exceed  50  to  100  times  the  volume  of  the  specimen  to  be  preserved.  2.  The 
fluid  must  always  be  clear.  As  soon  as  it  becomes  clouded  it  must  be  replaced 
by  fresh  fluid.  The  clouding  often  begins  within  an  hour  after  the  introduction 
of  the  specimen.  3.  The  specimens  to  be  preserved  should  be  as  small  as 
possible ;  in  general,  not  exceeding  i  to  2  c.c.  Should  the  fixation  of  the 
entire  object  be  necessary  [e.  g.,  for  after-orientation),  make  many  deep  inci- 
sions into  it,  one  to  two  hours  after  it  has  been  introduced.  It  should  not  lie 
in  the  fixing  fluid  on  the  bottom  of  the  vessel,  but  be  suspended  in  the  glass, 
or  placed  upon  a  layer  of  cotton  or  glass-wool. 

1.  Absolute  alcohol  is  very  suitable  for  glands,  skin,  blood-vessels,  etc. 
It  acts  at  the  same  time  as  a  means  of  hardening.  Specimens  fixed  in  abso- 
lute alcohol  can  be  sectioned  after  twenty- four  hours.* 

On  this  account  alcohol  is  especially  suitable  for  quick  preparation  of 
microscopical  specimens.  The  following  points  should  be  especially  noted  : 
I.  The  absolute  alcohol  must  be  changed  after  three  to  four  hours,  even  when 
it  is  not  clouded.  2.  Avoid  allowing  the  objects  to  lie  flat  upon  the  bottom 
of  the  vessel,  or  to  attach  themselves  to  it.f  They  should  either  be  sus- 
pended by  a  thread  in  the  alcohol  or  laid  on  a  small  pad  of  cotton  on  the 
bottom  of  the  glass. 

Weaker  alcohol  {e.  g.,  90  per  cent.)  acts  quite  differently,  shrivelling  the 
tissues,  and,  therefore,  cannot  be  employed  in  the  place  of  absolute  alcohol. 

2.  Chromic  acid  is  mainly  used  in  two  aqueous  solutions  : — 

(a)  As  o.  I  to  0.5  per  cent,  solution  (p.  20),  which  is  especially  suitable  for 
organs  which  contain  a  great  amount  of  loose  connective  tissue.     This  strong 

*One  should  not  too  long  delay  using  objects  preserved  in  absolute  alcohol,  for  the  ele- 
menls  deteriorate  gradually.  They  may  be  sectioned  after  three  to  eight  days.  Sections  of 
specimens  which  have  lain  only  twenty-four  hours  in  absolute  alcohol  are  likely  to  stain  poorly. 

t  The  portion  which  has  thus  been  in  contact  with  the  vessel  appears  strongly  compressed 
in  the  sections. 


28  HISTOLOGY. 

solution  gives  to  the  connective  tissue  a  superior  consistency,  but  has  the 
disadvantage  of  making  the  staining  difificult.  It  is  further  useful  for  fixing  the 
karyokinetic  figures.  The  specimens  remain  here  one  to  eight  days,  after 
which  they  are  placed  three  to  four  hours  in  running  water,  or,  if  that  is  not 
possible,  for  the  same  period  in  water  changed  three  to  four  times.  Then  they 
are  transferred  to  distilled  water  for  several  minutes  and  at  last  hardened  in 
gradually  strengthened  alcohol  protected  from  daylight  (§  5). 

(/^)  As  0.05  per  cent,  solution,  which  is  prepared  by  diluting  the  o.  i  per 
cent,  solution  with  an  equal  amount  of  distilled  water.  Treat  as  under  solu- 
tion (a),  except  that  the  objects  remain  only  twenty-four  hours  in  solution  (6). 

Chromic  acid  solution  penetrates  slowly.  Therefore,  only  small  pieces 
of  5  to  10  mm.  a  side  should  be  preserved. 

3.  Nitric  acid  as  3  per  cent,  solution  (3  c.c.  concentrated  nitric  acid 
[p.  20]  to  97  c.c.  distilled  water)  is,  like  the  strong  chromic  acid  solution,  an 
excellent  medium  for  organs  rich  in  connective  tissue.  The  objects  remain  five 
to  eight  hours  in  this  solution,  and  are  then  carried,  not  into  water,  but  directly 
into  alcohol  of  gradually  increased  strength,  for  hardening. 

4.  Kleincnherg  s  Fluid  {yt.  20). — Delicate  objects  (embryos)  maybe  allowed 
to  remain  five  hours  in  this  fluid,  and  more  solid  parts  twelve  to  twenty  hours. 
Then  for  hardening  they  are  transferred  to  gradually  strengthened  alcohol  (§  5) 
without  previous  washing. 

5.  Miillfr'' s  Fluid  {p.  20). — The  objects  are  placed,  for  one  to  six  weeks,* 
in  a  large  quantity  ( —  400  c.c.)  of  this  solution,  then  for  four  to  eight  hours 
washed  in  running  water,  rinsed  in  distilled  water,  and  finally  brought  into 
gradually  strengthened  alcohol  protected  from  daylight  (p.  29,  foot-note).  If 
one  fails  to  follow  with  painstaking  conscientiousness  the  above-specified  rules 
for  fixing,  he  will  secure  imperfect  results,  for  which  even  experienced  micro- 
scopists  have  held  the  blameless  Miiller's  fluid  responsible. 

6.  Osmic  Acid  Solution  (p.  21). — In  the  use  of  this,  care  should  be  taken 
not  to  inhale  its  irritating  vapor.  Fix  the  specimens,  either  by  placing  the 
moist  pieces  in  the  vapor  or  by  immersing  minute  pieces  (to  5  mm.  a  side)  in 
a  small  quantity  (i  to  6  c.c.)  of  the  acid  (most  used  in  i  per  cent,  solution).  To 
fix  by  means  of  the  vapor,  fill  a  test-tube  of  5  cm.  depth  with  i  c.c.  of  the 
2  per  cent,  solution  and  the  same  amount  of  distilled  water,  and  fasten  the 
specimen  with  quills  to  the  underside  of  the  cork  of  the  test-tube.  After  ten 
to  sixty  minutes,  according  to  the  size  of  the  specimen,  it  is  taken  from  the 
cork  and  placed  in  the  fluid  in  the  test-tube.  In  both  cases  the  objects  stay 
twenty-four  hours  in  the  acid,  and,  during  this  time,  the  tube  must  be  well- 
closed  and  kept  in  the  dark.  Then  the  objects  are  taken  out,  washed  in  run- 
ning water  for  one-half  to  two  hours,  rinsed  quickly  in  distilled  w-ater,  and 
hardened  in  alcohol  of  gradually  increased  strength  (§  5). 

7.  Chfomo-aceto-osmic  acid  {Flemming' s  solution')  (p.  21)  is  an  excellent 

*Oiie  can  keep  the  pieces  still  longer — up  to  six  months  in  Miiller's  Hiiiil.  They  can 
then  be  cut  and  stained  without  the  alcohol  hardening. 


THE    I'KKPARATION    OF    MICROSCOPICAL    SPECIMENS.  29 

medium  for  fixing  karyokinetic  figures.  Place  absolutely  fresh  pieces,  still  warm 
and  from  3  to  5  mm.  on  a  side,  in  4  c.c.  of  this  fluid  where  they  remain  one 
to  two  days  or  even  longer.  Then  the  pieces  should  be  washed  in  running 
water  for  one  hour  (or  better  longer),  rinsed  in  distilled  water,  and  hardened 
in  gradually  strengthened  alcohol  (§5). 

8.  Platino-aceto-osmic  mixture  {Hennann' s  solution)  is  very  useful  for 
displaying  shar|jly  defined  cell  boundaries.     It  is  used  as  Flemming's  fluid. 

The  fluids  used  for  fixing  cannot  be  used  again,  but  must  be  thrown  away. 

§  5.   H.\RDENING. 

Except  when  absolute  alcohol  is  used  the  above  methods  of  fixing  necessi- 
tate a  supplementary  process  of  hardening.  The  best  means  of  hardening  is 
by  gradually  strengthened  alcohol.  It  is  necessary  to  use  abundant  fluid  and  to 
change  the  alcohol  as  it  becomes  cloudy  or  colored.* 

The  following  is  the  exact  treatment  :  After  the  specimens  have  been  fixed 
in  one  of  the  above-enumerated  fluids  and  washed  in  water, f  they  should  be 
transferred  for  twelve  to  twenty  hours  to  70  per  cent,  alcohol  and  then  placed 
in  90  per  cent,  alcohol,  where,  after  twenty-four  to  forty-eight  hours  more,  the 
hardening  is  completed.  In  this  alcohol  the  specimens  may  remain  for  several 
months,  until  one  is  ready  to  use  them.  The  90  per  cent,  alcohol,  after  it  has 
been  used  for  hardening,  can  be  collected  for  burning  or  for  hardening  liver 
for  imbedding. 

§  6.  DECALCIFYING. 
The  specimens  to  be  decalcified  cannot  be  laid  fresh  into  the  decalcifying 
fluid,  but  must  first  be  fixed  and  hardened.  For  this  purpose,  lay,  in  300 
c.c.  of  Miiller's  fluid,  small  bones  up  to  the  size  of  a  metacarp,  entire  teeth, 
and  pieces  3  to  6  cm.  in  length  sawed  from  the  larger  bones.  After  lying  for 
two  to  four  weeks  in  Miiller's  fluid  and  having  been  washed,  these  pieces  are 
placed  in  150  c.c.  of  gradually  strengthened  alcohol.  After  remaining  three 
days,  or  longer  if  necessary,  in  90  per  cent,  alcohol,  they  are  transferred  into 
the  decalcifying  fluid,  /.  e.,  dilute  nitric  acid  (pure  nitric  acid  9  to  27  c.c. 
to  300  c.c.  distilled  water).  Large  quantities  (at  least  300  c.c.)  of  this 
fluid  should  be  used,  being  changed  at  first  daily,  and  later  every  four  days 
until  the  decalcification  is  complete.  The  degree  of  decalcification  may  be 
ascertained    by  cutting  with   an    old   scalpel. J     Decalcified    bone  is  elastic, 


*  If  not  washed  for  a  I0115;  lime  (and  tliat  must  be  avoided  because  of  the  danger  of  decom- 
position) the  pieces,  preserved  in  chromic  acid  and  in  Miiller's  fluid,  under  the  action  of  daylight 
fonn  a  precipitate.  The  alcohol,  therefore,  must  be  kept  in  the  dark  so  that  no  precipitate  shall 
be  formed.  In  tliat  case  the  alcohol,  though  remaining  clear,  becomes  yellow.  The  90  per 
cent,  alcohol  must  also  be  changed  daily  as  long  as  it  becomes  intensely  yellow. 

j-  \x\  exception  is  made  only  to  those  objects  which  have  been  fixed  in  3  per  cent,  nitric 
acid  and  in  picrosulphuric  acid.  These  should  l)e  transferred  directly  to  70  per  cent,  alcohol, 
which  nnist  be  changed  several  times  during  the  first  day. 

J  The  scalpel  should  be  at  once  carefully  cleaned. 


30  HISTOLOGY. 

soft,  and  can  be  easily  cut.  Fcetal  bones,  heads  of  embn'os  may  be  decalcified 
in  weaker  nitric  acid  (i  c.c.  of  pure  acid  [p.  20]  to  90  c.c.  distilled  water)  or 
in  500  c.c.  saturated  aqueous  picric  acid  solution  (p.  20).  The  decalcifying 
process  requires  several  weeks  with  thick  bones  ;  but  only  three  to  twelve  days 
with  small  and  fcetal  bones.  As  soon  as  the  decalcifying  is  completed,  the 
bones  are  washed  six  to  twelve  hours  in  running  water  and  afterward  hardened 
in  gradually  strengthened  alcohol  (§  5). 

Beginners,  not  seldom,  transfer  the  bone  to  alcohol  before  the  decalcifica- 
tion is  complete,  so  that  it  cannot  be  used  for  sectioning.  In  such  cases  the 
entire  decalcification  process  must  be  repeated.  On  the  other  hand,  specimens 
left  too  long  in  the  decalcifying  fluid,  will  be  entirely  destro\-ed. 

§  7.   SECTIONING. 

The  razor  (p.  18)  must  be  sharp,  for  success  in  sectioning  depends  largely 
upon  the  good  condition  of  the  knife.  In  cutting,  the  blade  must  be  wet  with 
alcohol.  (Water  is  not  suitable  for  this  purpose  for  it  does  not  adhere  evenly 
to  the  surface  of  the  blade.)  The  razor  should,  before  every  third  or  fourth 
section,  be  dipped  into  a  flat  dish,  filled  with  30  c.c.  90  per  cent,  alcohol, 
which  serves  at  the  same  time  as  a  receptacle  for  the  sections  which  have  been 
prepared.  The  razor  is  to  be  held  lightly,  in  a  horizontal  position,  with  the 
thumb  toward  the  sharp  edge,  the  fingers  toward  the  back  of  the  blade  and 
the  back  of  the  hand  upward.  First  a  smooth  surface  of  the  object  to  be 
sectioned  must  be  made  by  a  single,  rapid,  and  even  cut  of  the  razor. 
From  this  surface  a  large  number  of  sections,  one  after  another,  may  be 
prepared,  as  thick  as  desired.  The  sections  should  always  be  cut  with 
a  light,  not  too  quick,  movement,  as  smooth  and  as  evenly  thin  as  pos- 
sible. * 

It  is  always  desirable  to  make  ready  a  large  number  (10  to  20)  of  the 
sections,  which  may  be  transferred  to  a  glass  dish  by  floating  them,  with  the  aid 
of  a  needle,  off  from  the  blade  immersed  in  the  fluid,  f 

Then  place  the  dish  on  a  black  surface  and  search  out  the  best  sections. 
The  thinnest  sections  are  not  always  the  most  useful.  For  many  preparations, 
e.  g.,  for  sections  through  the  coats  of  the  stomach,  thicker  sections  are  to  be 
recommended.  For  a  general  view,  large  thick  sections  should  be  prepared  ; 
for  the  study  of  finer  structures,  the  thinnest  possible  sections.  If  the  object 
to  be  cut  is  too  small  to  be  handled  in  the  fingers,  then  it  should  be  imbedded. 
A  simple  method  of  imbedding  is  by  pressing  the  specimen  into  hardened  liver. 
For  this  may  be  used  either  ox  liver  or,  better,  human  fat-  or  amyloid-liver  (to 
be  obtained  from  the  pathological  laboratory).  |    This  should  be  cut  into  pieces 

*  In  doing  this  the  edge  of  the  razor  should  not  be  pressed  against  the  object  but  gently 
drawn  through  it  from  right  to  left. 

t  Very  fine  sections,  if  they  are  not  to  be  stained  or  if  they  are  already  stained,  can  best  be 
drawn  or  rinsed  from  the  inclined  edge  of  the  razor  directly  upon  the  slide. 

X  Dog's  liver  (to  be  obtained  from  the  physiological  laboratory)  is  also  recommended. 


THE    PREPARATION    OF    MICROSCOPICAL    SPECIMENS.  3 1 

3  cm.  high,  2  cm.  broad,  and  2  cm.  long,  and  thrown  immediately  into  90  per 
cent,  alcohol,  which  must  be  changed  the  next  day.  In  three  to  five  days  the 
liver  has  gained  the  necessary  hardness.  Now  in  one  of  these  pieces  an  incision 
should  be  made  from  the  top  to  the  centre  and  into  this  the  specimen  should 
be  pressed.  If  the  specimen  is  too  thick,  the  incision  may  be  enlarged  with  a 
small  scalpel.  The  object  needs  no  further  fixing,  other  than  perhaps  binding 
together  with  thread. 

I  am  accustomed  to  imbed  most  specimens  in  hardened  liver.  One  can 
thus  make  very  thin  sections,  at  least  with  a  certain  amount  of  practice  which 
can  be  acquired  in  a  few  weeks. 

§  8.  STAINING. 

Before  using  a  stain  it  should  always  be  filtered.  A  small  funnel  may  be 
made  by  simply  folding  twice  a  piece  of  filter-paper  5  cm.  sq.  and  sticking  it 
in  a  cork  frame.  To  make  this  frame,  cut  a  piece  2  cm.  sq.  from  the  centre 
of  a  cork-plate  5  cm.  sq.  The  cork  frame  should  be  placed  on  four  long  pins. 
Such  a  funnel  and  frame  can  be  used  many  times,  but  only  for  the  same  fluid. 
The  sections  should  not  swim  on  the  surface  of  the  staining  fluid,  but  be  sub- 
merged with  needles. 

I.   A'uclear  Staining  with  Bohmer'  s  Htematoxylin  (see  p.  22). — Filter  3  to 

4  c.c.  of  the  staining  fluid  into  a  watch-glass  and  place  the  sections  therein. 
The  time  required  for  staining  varies  greatly.  Sections  fixed  and  hardened  in 
alcohol  stain  in  one  to  three  minutes.  If  fixed  with  Miiller's  fluid  they  must 
remain  somewhat  longer  (to  five  minutes).* 

P'rom  the  stain  place  the  sections  in  a  watch-glass  in  distilled  water, 
rinse  (/.  c. ,  move  them  about  somewhat  with  a  needle  to  free  them  from  the 
surplus  stain),  and  after  one  to  two  minutes  transfer  them  to  a  large  dish  filled 
with  30  c.c.  distilled  w-ater.  Here  they  should  remain  at  least  five  minutes 
until  their  blue-red  color  has  gradually  changed  to  a  bright  dark  blue.  This 
color  will  be  the  purer  the  longer  the  sections  are  allowed  to  remain  in  water 
(even  to  twenty-four  hours). f 

Beginners  are  recommended  to  leave  the  sections  different  lengths  of  time, 
one,  three,  five  minutes,  in  the  stain  in  order  to  note  which  time  gives  the 
best  staining.  The  chief  essential  in  hematoxylin  staining  is  proper  rinsing. 
If  the  water  becomes  blue,  then  it  must  be  renewed.     The  used  stain  may  be 


*  Sectitins  fixed  in  strong  solution  of  chromic  acid  or  those  not  entirely  free  from  acid, 
stain  very  slowly,  at  times  not  at  all.  One  can  remedy  these  defects  by  either  keeping  the  speci- 
mens two  or  three  months  in  90  per  cent,  alcohol,  changed  two  or  three  times,  or  placing  them 
five  or  ten  minutes  in  a  watch-glass  with  5  c.c.  distilled  water,  having  added  3  to  7  drops 
of  35  per  cent,  caustic  potash.  Then  transfer  the  sections  to  a  watch-glass  with  fresh  dis- 
tilled water  for  one  or  two  minutes,  and  from  ihence  to  h;emato.\ylin.  After  five  to  ten  minutes 
these  sections  will  stain  also. 

t  At  first  the  sections  have  a  liiffiise  blue  tint.  The  differentiation  takes  place  usually  after 
five  minutes,  sometimes  not  for  hours. 


32  HISTOLOGY. 

poured  back  into  the  htematoxylin  bottle  through  filter-paper.  The  watch- 
glass  should  be  cleaned  at  once. 

H(e?nalum  (p.  22)  appears  to  render  still  better  service,  since  it  never  over- 
stains.  It  is  used  in  a  similar  manner,  requiring,  however,  a  somewhat  longer 
time  for  staining,  often  as  much  as  ten  minutes. 

2.  Nuclear  Staining  with  Alum  Carmine  (p.  23). — Filter  3  to  4  c.c.  of 
stain  into  a  watch-glass  and  place  the  sections  therein  for  at  least  five  minutes. 
The  advantage  of  this  stain  lies  in  the  fact  that  the  sections  can  remain  some- 
what longer  in  the  solution  without  becoming  overstained,  as  easily  happens  in 
hsematoxylin.  A  disadvantage  is  that  the  alum  carmine  is  a  pure  nuclear 
stain,  while  hsematoxylin  gives  the  protoplasm  also  a  grey  or  grey-violet  tint, 
thereby  rendering  it  easily  recognizable. 

3.  Diffuse  Staining. — For  staining  protoplasm  and  intercellular  substance  : 
(a)  Slow  Stain. — A  small  drop  of  neutral   carmine  solution   (p.  23)  is 

brought  by  a  glass  rod  to  a  dish  filled  with  20  c.c.  distilled  water,  on  the  bot- 
tom of  which  lies  a  small  piece  of  filter-paper.  * 

The  sections  stay  over  night  in  the  fluid.  The  weaker  the  stain  the  longer 
the  sections  need  to  remain  in  it  and  the  more  effective  the  staining.  The  begin- 
ner is  always  inclined  to  consider  the  pale  pink  solution  too  weak  to  produce  a 
good  stain,-until  on  the  next  day  the  dark  pink  or  red  sections  teach  him  better. . 

This  stain  by  itself  can  be  used  in  only  a  few  cases,  but  is  to  be  recom- 
mended for  double  staining.  In  the  latter  case  stain  first  with  the  carmine 
solution  and  then  with  hsematoxylin. 

{F)  Rapid  Staining. — Add  10  drops  of  the  eosin  solution  (p.  23)  to  3  to  4 
c.c.  distilled  water.  The  sections  remain  one  to  five  minutes  in  it,  then  are 
quickly  rinsed  in  a  watch-glass  with  distilled  water  (see  Haematoxylin  Staining) 
and  placed  for  ten  minutes  in  30  c.c.  distilled  water.  The  stain  may  be  used 
alone  or  combined  with  hfematoxylin,  in  which  case  the  whole  process  of 
haematoxylin  staining  is  to  be  carried  out  first  and  then  that  of  eosin  staining. 

4.  Staining  of  the  Chromatin  Substance  (for  karyokinetic  figures). — The 
specimens  are  placed  for  five  to  ten  minutes  in  a  dish  with  10  c.c.  distilled  water 
and  one  drop  of  pure  hydrochloric  acid  ;  next  washed  off"  in  distilled  water  one 
minute,  then  laid  for  five  minutes  in  a  watch-glass  of  saffranin  solution  (see 
p.  23).  The  sections  or  membranes  are  taken  out  with  a  needle  and  placed 
in  5  c.c.  absolute  alcohol,  to  be  differentiated.  When  the  sections  give  off  no 
more  color  (usually  in  one  and  a  half  to  two  minutes)  they  are  transferred  to 
5  c.c.  fresh  absolute  alcohol,  and,  after  a  minute  longer,  are  cleared  and  mounted 
in  balsam  (see  §  10,  3,  p.  39).  A  stay  too  prolonged  in  the  absolute  alcohol 
may  lead  to  total  decolorization.  Unsuccessful  staining  is  due  usually  to  an  in- 
sufficient amount  of  acetic  acid  in  the  Flemming's  fluid  (p.  21,  foot-note). 

5.  Staining  in  Bulk. — Nuclear  staining  of  the  whole  specimen  before  sec- 
tioning. 

The  fixed  and  hardened  specimens  are  placed  in  30  c.c.  borax-carmine  for 

*  If  the  filter-paper  is  omitted  the  sections  stain  only  on  one  side. 


THE    I'KF.I'AkATlON    I1F    MICKDSCOPICAI,    SPECIMENS.  33 

twenty-lour  hours  if  they  are  small  (5  mm.  square)  or  for  two  to  three  days 
if  they  are  larger.  (The  used  stain  may  be  returned  to  its  bottle.)  From  this 
they  are  transferred  directly  to  25  c.c.  70  per  cent,  acidulated  alcohol  (p.  23) 
which,  after  a  few  minutes,  grows  red  *  and  must  then  be  renewed. 

After  about  fifteen  minutes  the  alcohol  is  again  changed.  This  is  repeated 
until  the  fluid  is  no  longer  colored,  f  The  piece  is  then  transferred  to  90  per 
cent,  alcohol,  and  if  it  is  not,  after  twenty-four  hours,  hard  enough  to  cut,  it 
is  placed  for  another  twenty-four  hours  in  absolute  alcohol. 

6.  Picrocarmine.  Double  Staining. — Nuclei  and  connective  tissue  red, 
protoplasm  yellow. 

About  5  c.c.  of  the  fluid  are  filtered  into  a  watch-glass.  The  length  of 
time  necessary  for  the  action  of  picrocarmine  is  very  different  for  individual 
oljjects  and  can  be  given  appro.ximately  only  in  the  special  directions.  .\t  the 
end  of  the  process  the  stain  is  filtered  back  into  the  bottle  and  the  specimens 
transferred  to  10  c.c.  distilled  water  for  ten  to  thirty  minutes.  (This  rinsing 
is  omitted  in  staining  under  the  cover  glass;  p.  41.)  If  the  specimen  {e.  g.,  a 
section)  is  to  be  dehydrated  in  absolute  alcohol  (see  p.  39),  it  should  not  remain 
longer  than  one  to  two  minutes,  as  the  alcohol  extracts  the  yellow  stain.  \ 

Picrocarmine  is  u.sed  chiefly  in  examining  fresh  specimens.  If  the  solu- 
tion is  good,  a  very  pretty  staining  is  obtained  and  the  outlines  may  be  yet 
more  sharply  brought  out  by  the  addition  of  acid  glycerine  (see  p.  41). 

7.  Nuclear  Staining  with  Aniline  Dyes. — The  best  aniline-stains  for  this 
purpose  are  vesuvin  and  methylviolet  B.      (See  p.  23.  ) 

Filter  5  c.c.  of  the  fluid  into  a  watch-glass.  The  sections  placed  in  this 
stain  become  quite  dark  in  two  to  five  minutes,  and  are  then  washed  off  quickly 
in  5  c.c.  distilled  water  and  transferred  to  a  watch-glass  of  absolute  alcohol, 
where  they  give  off  much  color.  After  a  few  minutes  (three  to  five)  the  sec- 
tions become  clearer,  and  even  with  the  unaided  eye  certain  parts,  e.  g.,  the 
glands  in  the  skin,  may  be  recognized.  Now-  the  sections  are  placed  in  a  sec- 
ond watch-glass  of  5  c.c.  absolute  alcohol,  and  after  two  minutes  cleared  and 
mounted  in  damar-varnish  (p.  39).  The  result  is  a  very  beautiful  permanent 
nuclear  staining.  A  disadvantage  lies  in  the  necessity  for  using  so  much 
alcohol. 

Saffranin  can  be  similarly  employed.  The  .sections  stained  for  five  min- 
utes are  rinsed  quickly  (one-half  minute)  in  a  watch-glass  with  absolute  alco- 
hol, and  then  transferred  to  a  second  glass  of  absolute  alcohol,  which  must 
be  renewed  as  soon  as  it  becomes  an  intense  red.     After  five  to  fifteen  minutes 


*  Specimens  li.\e<l  in  Miiller's  fluid  give  off  very  little  stain. 

t  These  changes  may  require  one  to  three  days.  The  alcohol  should  be  renewed  every 
two  hours  the  first  day  and  every  four  hours  thereafter.  If  one  wishes  to  be  economical  he  cin 
slowlypush  the  specimen  with  a  needle  out  of  the  red  fluid  area  in  which  it  lies  into  an  unstained 
portion  of  the  lluid. 

I  One  can  prevent  the  decolorization  by  tlnowing  into  the  watch-glass  of  absolute  alcohol 
a  small  picric-acid  crystal. 


34  HISTOLOGY. 

(the  time  varies  with  the  thickness  of  the  sections)  the  sections  become  lighter, 
and  are  then  cleared  and  mounted  in  damar-varnish  (p.  39). 

8.  Methylene  blue  for  staining  axis-cylinders. 

The  method  is  to  be  used  only  for  absolutely  fresh  specimens.  Prepare  a 
dilute  (jV  per  cent.)  solution  by  adding  15  c.c.  distilled  water  to  i  c.c.  of  the 
I  per  cent,  solution  (p.  23).  From  this  a  few  drops  are  applied  to  the  fresh 
preparation  lying  upon  the  slide  and  lightly  covered  with  a  watch-glass.* 

After  one  to  one  and  one-half  hours  the  reaction  begins.  To  prevent  drying 
during  this  period  add  from  time  to  time  a  drop  of  the  diluted  staining  solu- 
tion, or  of  normal  salt  solution.  Then  put  on  the  cover-glass.  By  this  pro- 
cess the  axis-cylinder  stains  a  beautiful  blue  color.  Still  other  elements,  as 
nuclei,  connective-tissue  fibres,  etc.,  and,  if  the  specimen  remains  longer  in 
the  solution,  even  the  medullary  sheaths  of  the  nerves  are  stained.  For  pre- 
serving the  preparation,  the  staining  solution  is  replaced  after  the  method 
given  on  p.  41,  by  a  few  drops  of  a  solution  of  picrate  of  ammonia  (p.  23), 
the  blue  color  changing  thereby  to  violet.  Then  a  drop  of  glycerine  is  allowed 
to  pass  under  the  cover-glass.  After  eighteen  to  twenty  hours  still  more  solu- 
tion of  picrate  of  ammonia  is  added  to  the  glycerine,  and  the  cover-glass 
secured  by  cement  (p.  22).  The  preparations  must  not  be  left  long  in  the 
sunlight,  or  they  will  fade,  and,  in  any  case,  soon  lose  their  original  beauty. 

9.  Mucous  sfaining  with  Delafiehf  s  hatnatoxylin. 

Filter  into  a  watch-glass  filled  with  25  c.c.  distilled  water  3  drops  of 
this  hasmatoxylin  (p.  22).  In  this  dilute  solution  the  sections  (best  those 
specimens  fixed  in  Flemming's  fluid)  f  are  placed  for  two  to  three  hours. 

Usually  after  this  period  the  mucus,  e.  g.,  in  goblet-cells,  is  already  an 
intense  blue,  which  can  be  ascertained  by  examining  even  with  low  power  the 
sections  as  they  lie  in  the  solution.  It  is  often  necessary  for  the  sections  to 
remain  a  long  time  in  the  solution.  Then  the  sections  are  rinsed  one  minute, 
and,  after  the  rule  given  (§  10,  3,  p.  39),  mounted  in  damar-varnish.  The 
nuclei  stain  blue  also.  A  very  pretty  effect  is  produced  in  combination  with 
saffranin  and  picric  acid.     This 

10.  Triple  staining  is  obtained  in  the  following  manner  :  The  sections 
stained  in  Delafield's  h<emato.xylin  are  transferred  for  five  minutes  to  saffranin 
(p.  23),  then  to  5  c.c.  absolute  alcohol,  which  is  changed  twice  in  fifteen 
minutes.  Then  the  section's  are  placed  for  a  minute  in  5  c.c.  absolute 
alcohol,  to  which  is  added  5  drops  of  saturated  alcoholic  picric  acid  solution 
(i  gm.  picric  acid  to  15  c.c.  absolute  alcohol).  They  are  then  rinsed  in 
pure  absolute  alcohol  one-half  minute  and,  after  rule  §  10,  3,  p.  39, 
mounted  in  damar-varnish.  Result :  mucus  blue,  nuclei  red,  protoplasm, 
fibres  yellow. 


*The  cover-glass  should  not  be  closed  hermetically,  for  the  access  of  air  is  necessary  for 
the  success  of  the  staining.  By  gently  moving  the  preparation  to  and  fro  the  action  may  be 
started. 

t  Specimens  fixed  in  Miiller's  fluid  are  also  suitable  for  mucus  staining. 


THE    PREPARATION"    OF    MICROSCOPICAL    SPECIMEN'S.  35 

n.  Silver  Staining. — For  exhibition  of  cell  outlfnes,  staining  of  the  inter- 
cellular substance.* 

The  use  of  metal  instruments  is  to  be  avoided.  Use  glass  rods  and  in- 
stead of  needles  take  quills. 

The  specimen  is  placed  in  lo  to  20  c.c.  of  i  per  cent.,  or  weaker  (see 
Special  Technique)  solution  of  silver  nitrate  (p.  21)  for  one-half  to  ten  min- 
utes, according  to  its  thickness.  It  is  then  taken  with  glass  rods  out  of  the 
fluid,  which  has  meanwhile  become  milky,  rinsed,  placed  in  a  large  white  dish 
(  a  porcelain  plate)  with  100  c.c.  distilled  water,  and  e.xposed  to  direct  sunlight. 
After  a  few  minutes  a  slight  browning  appears,  the  sign  of  successful  reaction. 
As  soon  as  the  specimen  becomes  a  dark  red-brown,  usually  after  five  to  ten 
minutes,  it  is  taken  out,  transferred  for  five  to  ten  minutes  to  a  watch-glass 
with  distilled  water  to  which  a  few  grains  of  common  salt  have  been  added. 
It  is  then  placed  in  30  c.c.  70  per  cent,  alcohol  in  the  dark.  After  three  to 
ten  hours  the  70  per  cent,  is  replaced  by  90  per  cent,  alcohol.  The  specimen 
must  be  kept  away  from  the  light  while  in  the  silver  solution.  The  reduction 
on  the  contrary  should  only  be  brought  about  in  direct  sunlight,  t 

If  the  sun  does  not  shine,  place  the  specimen,  which  has  been  taken  out 
of  the  silver  solution  and  quickly  rinsed  in  distilled  water,  in  the  dark  in  30 
c.c.  70  percent,  (later  90  per  cent.)  alcohol,  and  it  may  be  exposed  to  the 
next  sunlight. 

GolgV s  viethodX  for  demonstration  of  the  elements  of  the  nervous  system. 

The  method  unites  fixing  and  staining.  The  objects  must  be  as  fresh  as 
possible.     Their  diameter  should  in  general  not  exceed  4  mm.     It  is,  however, 

*  Crossmarkings,  which  under  treatment  with  silver  nitrate  appear  in  the  different  tissue 
elements  and  organs,  especially  in  nerve-fibres,  blood-vessels,  in  cartilage,  etc. ,  are  artificial 
products  of  the  stift'ening  and  acidifying  action  of  silver  nitrate  u]M)n  colloid  structures. 

f  The  reduction  takes  place  also  in  ordinary  daylight,  but  only  slowly,  and  shows  less  dis- 
tinct outlines. 

+  Editor^ s  Remark. — In  American  laboratories  a  modification  of  the  (jolgi  method,  by  Cox, 
is  often  used  with  excellent  results.  This  method  may  be  specially  recommended  to  beginners, 
because  its  management  is  very  simple  and  almost  always  successful.  Unfortunately  this  method 
is  not  applicable  for  younger  embryonic  tissues.  In  using  it  the  following  directions  must  be 
observed  :  Put  pieces,  2  centimeter  cubes  or  smaller,  of  the  central  nervous  system  of  adult  or 
new-born  animals  into  the  Cox-Golgi  mix/iirf,  whose  composition  is  given  on  p.  20,  retiiark, 
for  six  to  ten  weeks.  Use  10  to  20  times  the  volume  of  the  tissue  to  be  hardened.  Change  the 
fluid  after  twenty-four  hours,  three  days,  eight  days,  fifteen  days,  twenty-one  days,  and  thirty 
days.  Keep  the  pieces  in  the  fluid  till  ready  to  cut.  Specimens  will  keep  in  good  condition 
about  ten  months.  The  preparations  for  cutting  arc  the  following  :  Put  the  pieces  from  the  Cox- 
(Jolgi  mixture  directly  in  alcohol  of  95  per  cent,  for  one  hour,  in  alcoholelher  (e()ual  parts)  for 
half  an  hour,  in  thin  celloidin  solution  (in  alcohol-ether)  for  one  hour.  Then  mount  the  pieces 
on  a  block  in  celloidin  (see  Microtome  Technique)  and  harden  in  alcohol  of  80  per  cent,  for  one  to 
two  hours.  Cut,  at  once,  rather  thick  sections  (50  to  100  u).  Clear  the  sections  in  a  mixture  of 
xylol  3  parts  and  phenol  I  part,  in  which  they  may  be  kept  for  weeks  without  injury.  Mount 
in  balsam  and  cmier  the  seclions  with  a  c<n.'er-glass.  After  a  time  the  specimens  thus  preserved 
are  not  seldom  marred  by  the  appearance  of  corrosive  crystals,  but  the  impregnation  of  the 
elements  of  the  nervous  tissue  keeps  in  good  condition. 


36  HISTOLOGY. 

not  easy  to  cut  pieces  of  this  size  of  brain  and  other  soft  objects  without  crush- 
ing the  delicate  tissue.  For  this  reason,  larger  pieces  (3  cm.  a  side)  should 
be  laid  in  a  dish  of  Golgi's  mixture  freshly  prepared  (p.  20),  covered  and 
set  in  the  dark,  in  winter  in  a  warm  chamber  at  25°  C.  After  one  to  two 
hours  the  pieces  may  easily  be  cut  into  slices  4  mm.  in  diameter.  The  amount 
of  Golgi  fluid  is  to  be  regulated  after  the  number  of  slices,  each  slice  requiring 
about  10  c.c.  After  two  to  six,  seldom  as  many  as  fifteen  days  *  the  slices 
should  be  taken  out,  rinsed  rapidly  a  few  seconds  in  distilled  water,  dried 
gently  on  filter  paper  and  laid  f  in  acidulated  silver  solution  (10  c.c.  for  each 
slice).  A  brown  precipitate  covers  immediately  the  pieces.  It  is  sufficient  to 
leave  them  two  days  in  the  silver  solution,  which  does  not  need  to  stand  in  the 
dark  and  jimsf  not  be  placed  in  the  warm  chamber.  The  pieces  can,  however, 
remain  therein  for  six  days  without  injury.  Then  they  go  into  20  c.c.  absolute 
alcohol  for  fifteen  to  twenty  minutes  (not  longer).  They  are  then  imbedded 
in  elder  pith  (or  in  celloidin,  see  Microtome  Technique)  and  cut  in  thick 
sections  (p.  30). 

In  order  to  ascertain  which  may  be  utilized  each  section  is  examined  at 
once,  without  cover-glass  and  with  low  power,  and  if  suitable  transferred  to  a 
watch-glass  of  absolute  alcohol  one  to  two  minutes,  next  to  creosote  two 
minutes,  and  then  to  bergamot  oil  two  minutes.  From  this,  the  section  goes  a 
few  seconds  in  xylol,  and  then  upon  the  slide.  The  xylol  may  be  removed  by 
gently  pressing  filter  paper  on  the  section.  A  drop  of  balsam  which  is  thinned 
with  xylol  is  then  added  to  the  preparation.  A  cover-glass  must  not  be  laid 
on  it  because  thereby  the  moisture  in  the  preparation  is  prevented  from  evapor- 
ating which  spoils  the  Golgi  preparations.  Occasionally,  when  the  xylol  is  not 
sufficiently  removed,  the  Canada  balsam  gradually  withdraws  from  the  prepara- 
tions. These  appear  to  be  spoiled,  but  by  adding  another  drop  of  balsam  they 
are  completely  restored.  Examine  first  with  low  power.  When  the  balsam  is 
dry  the  high  power  can  be  used. 

The  results  with  this  method,  if  successful,  are  excellent.  Single  elements 
of  the  nervous  system  (never  all)  stand  out  sharply  black  on  a  light  back- 
ground. But  the  method  is  also  accompanied  with  undesirable  effects.  At 
times  blood-  and  lymph-vessels,  fibres  of  connective  tissue,  secretion,  mus- 
cular fibres,  and  epithelial  cells  are  blackened  and  almost  ahvays  the  best 
sections  are  disfigured  by  a  black  precipitate.  Fortunately  this  appears  on  the 
edges  of  the  preparations.  To  avoid  this  the  fresh  specimens  may  be  furnished 
with  a  coating  of  clotted  blood.  Very  often  the  reaction  fails  entirely, 
especially  when  the  specimens  have  remained  too  long  in  the  Golgi  mixture. 
Then  the  so-called  "  double  method  "  maybe  applied,  that  is  to  say,  the  speci- 
mens (if  the  first  sections  show  nothing)  are  placed  a  second  time  in  the  Golgi 
mixture  for  twenty-four  to  thirty-six  hours  and  just  as  long  in  the  silver  solution. 

*  For  this  see  special  directions. 

t  The  used  Golgi  mixture  is  to  be  thrown  away. 


THE    PREPARATION    OK    MICROSCOPICAL    SPECIMENS.  37 

After  a  second  failure  we  may  sometimes  succeed  by  a  third  repetition  of  the 
process.  Practice  and  patience  are  important  factors  in  the  use  of  this 
method. 

One  can  also  "  fix  "  the  preparations  blackened  in  this  way.  For  this  pur- 
pose the  sections  are  taken  from  the  alcohol  and  placed  in  a  mixture  of  lo  c.c. 
absolute  alcohol*  and  20  c.c.  of  diluted  hydrochinin  solution  for  five  minutes, 
where  they  become  dark  gray  to  black.  When  the  reduction  is  accomplished 
the  sections  are  transferred  directly  to  a  dish  of  70  per  cent,  alcohol  for  ten  to 
fifteen  minutes.  There  they  become  lighter,  and  then  go  for  five  minutes  into 
the  soda  solution  (p.  20,),  and  at  last  into  a  large  dish  of  distilled  water,  where 
they  must  remain  at  least  twenty-four  hours.  Thus  treated,  Golgi  jjreparations 
will  last  like  any  other  preparations  and  can  be  ]jreserved  under  a  cover-glass. 
They  may  be  successfully  stained  with  alum  carmine  and  hoematoxylin. 

13.    Gold  Staining. — For  demonstration  of  nerve-terminations. 

Steel  instruments  should  not  be  used.  All  manipulation  in  the  gold  solu- 
tion are  to  be  performed  with  glass  needles  or  rods. 

Heat  in  a  test-tube  S  c.c.  of  the  i  per  cent,  gold  chloride  solution  2  c.c. 
formic  acid  to  boiling  point  three  times.  Into  the  cooled  mixture  very  small 
pieces  (largest  5  mm.  a  side)  are  laid  for  an  hour  (to  be  kept  in  the  dark), 
then  quickly  rinsed  in  a  watch-glass  in  distilled  water  and  set  in  the  light  (not 
sunlight)  in  a  mixture  of  10  c.c.  formic  acid  and  40  c.c.  distilled  water. 
(Thereby  the  pieces  become  dark  violet  on  the  outside. )  The  reduction  fol- 
lows very  slowly,  often  after  twenty-four  to  forty-eight  hours.  The  pieces  are 
then  transferred  to  30  c.c.  70  per  cent,  alcohol,  and,  on  the  following  day, 
])laced  in  an  equal  quantity  of  90  jier  cent,  alcohol,  where,  to  hinder  a  further 
reduction,  they  must  remain  in  the  dark  at  least  eight  days. 

S  9.   INJECTING. 

Filling  the  blood-  and  lymph-vessels  with  colored  matters  is  a  special  art 
which  can  be  acquired  only  by  a  great  deal  of  practice.  Many  of  the  little 
devices  used  can  hardly  be  learned  from  written  directions,  however  explicit. 
Here  practical  knowledge  is  indispensable.  Therefore,  I  think  it  better  to 
omit  entirely  extensive  directions  for  injecting  in  this  book,  which  is  intended 
only  for  beginners. 

He  who  will  attempt  to  inject  must  have  an  exactly-working  hand-syringe, 
provided  with  easy-moving  piston  and  Canute  of  different  thicknesses.  As  in- 
jecting material  I  recommend  Berlin  blue  of  Griibler  (p.  19),  3  gm.  dissolved  in 
600  c.c.  distilled  water.  It  is  best  to  begin  with  the  injection  of  a  single 
organ,  e.  g.,  the  liver,  which  has  the  advantage  of  furnishing  useful  results,  even 
though  it  is  imperfectly  filled.  Fix  the  injected  objects  two  to  four  weeks  in 
Miiller's  fluid  (p.  28),  and  harden  them  in  gradually  strengthened  alcohol 
( p.  29).     The  sections  should  not  be  cut  too  thin. 


*  If  one  takes  too  much  alcohol  a  precipitate  appears,  which,  by  addition  of  hydrochinin 
solution,  can  be  quickly  removed. 


38  HISTOLOGY. 

§  10.   MOUNTING  AND  PRESERVING  OF  THE  PREPARATIONS. 

The  sections  treated  after  the  above-given  directions  are  now  ready  to  be 
transferred  for  microscopical  examination  to  a  slide  and  to  be  provided  with  a 
cover-glass.  The  fluids  in  which  the  sections  are  placed  for  this  purpose  are 
either:  i,  -water,  or  (if  one  desires  to  clear  or  preserve  the  sections),  2, 
glycerine,  or,  3,  damar-varnish. 

To  transfer  the  specimen  to  the  slide,  first  place  a  small  drop  of  the  fluid 
to  be  used  on  the  middle  of  the  slide ;  then  take  the  specimen  with  the  section 
lifter  and  slip  it  off  with  needles  upon  the  slide.  Very  fine  sections  are  lifted 
better  with  the  end  of  a  glass  rod,  by  rolling  which  they  are  brought  on  to  the 
slide.  The  section  will  then  lie  out  smoothly  and  may  be  covered  with  a 
cover-glass.* 

The  cover-glasses  must  be  grasped  edgewise,  not  touching  the  surface. 
In  covering  the  specimen  the  cover-glass  should  be  set  down  with  the  left  edge 
upon  the  slide,  and  then  slowly  lowered  upon  the  preparation,  while  its  under 
surface  is  supported  by  a  needle  held  in  the  right  hand.  A  still  simpler  method 
is  to  place  a  drop  of  the  fluid  in  question  on  the  lower  side  of  the  cover-glass 
and  let  it  drop  gently  down  upon  the  preparation.  The  fluid  in  which  the 
section  is  placed  should  occupy  the  entire  space  between  cover-glass  and  slide. 
If  there  is  not  enough  fluid  {i.  e.,  if  numerous  air  bubbles  appear  under  the 
cover-glass)  place  another  drop  of  fluid  at  the  edge  of  the  cover-glass  with  the 
end  of  a  glass  rod.  If  there  is  now  too  much  fluid  (and  therein  the  beginner 
especially  is  apt  to  err),  that  which  is  pressed  out  from  under  the  edge  of  the 
cover-glass  must  be  removed  with  filter  paper.  The  upper  surface  of  the  cover- 
glass  must  always  be  dry.  Small  air  bubbles  under  the  cover-glass  are  removed 
by  carefully  raising  and  lowering  it  several  times  with  a  needle  (see,  further, 
p.  40). 

Ad  I.  One  should  never  neglect  to  observe  unstained,  as  well  as  stained, 
sections  in  water  or  normal  salt  solution  (p.  19),  for  by  this  means  many  pecu- 
liarities of  structure  are  sharply  brought  out,  while  they  are  likely  to  escape 
observation  under  the  clearing  influence  of  glycerine  or  of  damar-varnish. 
Specimens  examined  in  water  or  in  salt  solution  cannot  be  kept  long. 

Ad.  2.  Preparations  examined  in  glycerine  can  be  preserved.  To  pre- 
vent the  shifting  of  the  cover  glass  it  may  be  fixed  with  cover-glass  cement  (see 
p.  22).  Before  this  can  be  done  the  edge  of  the  cover-glass  must  be  perfectly 
dry,  for  the  cement  adheres  only  to  the  dry  surface  of  the  glass.  The  slide 
may  be  dried  around  the  cover-glass  by  first  removing  the  superfluous  glycerine 
with  filter  paper,  and  then  by  carefully  wiping  with  a  cloth  moistened  in  90 


*  Examinations  with  low  power,  without  the  cover-glass,  are  designed  only  for  the  most 
superficial  orientation,  «■.  ^.,  to  see  whether  a  specimen  has  been  sufficiently  teased.  In  all 
other  cases  the  cover-glass  is  indispensable. 

Many  a  good  specimen,  if  one  neglects  to  cover  it,  appears  useless.  Examinations  with 
high-power  objectives,  without  a  cover-glass,  are,  in  general,  not  allowable. 


THE    PREPARATION    OF    MICROSCOPICAL    SPECIMENS.  39 

per  cent,  alcohol  and  held  over  the  end  of  the  finger,  taking  care  not  to  touch 
the  cover-glass.  Next  heat  a  glass  rod  and  dip  it  into  the  hard  cement,*  place 
a  drop  of  the  cement  on  each  corner  of  the  cover-glass,  and  trace  a  complete 
frame  about  the  glass  in  such  a  way  that  the  cement  covers  as  well  the  cover- 
glass  as  the  slide  to  an  extension  of  i  to  3  mm.  Lastly,  smooth  the  surface  of 
the  frame  with  the  reheated  rod. 

Specimens  preserved  in  glycerine  often  become  transparent  only  after  the 
second  or  third  day.  Hnsmatoxylin  and  other  stains  fade  after  a  short  time  ; 
picrocarmine  and  carmine,  on  the  other  hand,  are  lasting  in  this  fluid. 

Alt.  J.  The  mounting  of  objects  in  damar-varnish  is  the  usual  preserving 
method.  Damar-varnish  has  an  advantage  over  glycerine  in  that  it  preserves 
the  colors  of  the  specimens,  but  has  also  the  disadvantage  of  clearing  the 
preparation  much  more  than  the  dilute  glycerine,  thereby  rendering  many 
fine  structural  details  entirely  invisible. 

The  sections  jilaced  in  w-ater  or  alcohol  of  90  or  less  per  cent,  cannot, 
without  farther  special  treatment,  be  placed  in  damar-varnish.  They  must  first 
be  dehydrated.  For  this  purpose  the  sections  are  placed  by  means  of  a  needle 
(very  thin  sections  with  the  section-lifter)  into  a  covered  watch-glass  with  5 
c.c.  absolute  alcohol.  In  doing  this  the  least  possible  water  should  adhere  to  the 
sections.  If  a  spatula  is  used,  remove  the  water  from  it  with  filter-paper.  If 
the  section  is  transferred  with  a  needle  the  water  can  be  removed  at  the  same 
time  by  lightly  touching  the  section  with  filter  paper.  They  stay  in  absolute 
alcohol  two  minutes  (thin  sections) — ten  minutes  (thick  sections)  or  longer,  f 
Then  the  sections,  free  as  possible  from  alcohol,  are  transferred  for  clearing  into 
a  watch-glass  with  3  c.c.  bergamot  oil.  \  Place  the  glass  on  black  paper  so  as 
to  observe  better  the  growing  transparency  of  the  sections.  Avoid  breathing 
into  the  watch-glass,  for  an  immediate  clouding  of  the  bergamot  oil  takes  place. 
If  portions  of  the  section,  after  two  to  three  minutes,  have  not  become  trans- 
jjarent  (such  spots  appear  cloudy  in  direct  light,  dark  brown  in  transmitted 
light),  this  indicates  that  the  section  was  not  sufficiently  dehydrated,  and  hence 
that  it  must  be  put  back  in  absolute  alcohol.  After  being  completely  cleared  the 
section  is  transferred  to  the  dry  slide  and  the  superfluous  oil||  carefully  removed 

*  The  glass  rods  crack  very  easily  by  heating;  still,  they  are  preferable  to  metal  rods, 
which  cool  off  too  quickly.  The  cracking  can  be  somewhat  prevented  by  heating  the  rod  to  a 
rod  heat,  meanwhile  turning  it  constantly,  for  only  rods  which  have  been  suddenly  heated  crack 
when  dipped  into  the  cement. 

f  For  beginners  may  be  recommended  to  place  the  sections  taken  from  water  in  5  c.c.  90 
per  cent,  before  placing  them  in  the  same  amount  of  absolute  alcohol. 

\  Fine  sections  may  be  transferred  directly  from  absolute  alcohol  to  the  slide,  where,  after 
removing  the  supertluous  alcohol  with  filter  paper,  a  drop  of  bergamot  oil  is  to  be  added.  At 
first  the  oil  will  always  retire  from  the  section  and  must  be  brought  back  with  a  needle.  After 
the  completion  of  the  clearing  process,  which  one  can  ascertain  with  the  low  power,  the  excess 
of  oil  is  wiped  off  and  a  cover-glass  with  damar-varnish  added.  When  examining  uncov- 
ered sections  lying  in  oil,  both  sections  and  oil  may  become  cloudy  as  a  result  of  breathing  upon 
them.      In  this  case  let  the  clouded  oil  run  off  and  replace  it  with  a  drop  of  new  oil. 

II  The  oil  used  for  clearing  in  the  watch  glass  can  be  turned  back  into  the  lioltle. 


40  HISTOLOC;V. 

with  filter-paper  or  with  a  piece  of  linen  stretched  over  the  index  finger.* 
Then  the  cover-glass  with  a  drop  of  damar-varnish  adhering  to  its  under  surface 
is  placed  upon  the  specimen.  If  several  sections  are  to  be  placed  under  one 
cover-glass,  arrange  them  close  together  with  a  needle,  then  spread  with  a  glass- 
rod  an  evenly  thin  coat  of  the  varnish  on  the  under  side  of  the  cover-glass  and 
drop  it  on  the  sections.  Large  air  bubbles  are  driven  out  by  addition  of  a 
small  drop  of  damar-varnish  at  the  edge  of  the  cover-glass.  Within  a  day  the 
bubbles  disappear.  The  small  bubbles  disappear  spontaneously,  and  can  for 
this  reason  be  neglected. 

Beginners  not  seldom  find  that  the  varnish  becomes  cloudy  and  finally 
renders  the  preparation  partially  or  entirely  untransparent.  The  reason  for 
this  is  that  the  sections  were  not  entirely  dehydrated.  In  the  case  of  slight 
clouding,  which  under  the  microscope  is  seen  to  be  due  to  minute  drops  of 
water,  it  is  often  sufficient  to  warm  the  slide  a  little.  If  the  specimen  is  very 
cloudy  the  entire  slide  must  be  laid  for  one-half  hour  in  turpentine.  Then 
remove  the  cover-glass  carefully,  lay  the  section  for  two  minutes  in  turpentine  to 
loosen  the  adhering  varnish,  and,  finally,  to  complete  the  dehydration,  place  the 
preparation  in  4  c.c.  absolute  alcohol,  which  is  to  be  changed  after  five  minutes. 

Since  the  damar-varnish  dries  very  slowly  the  slides  should  not  stand  on 
edge  but  be  in  a  horizontal  position. 

The  series  of  processes,  which  a  fresh  specimen  has  to  undergo  before  it 
may  be  preserved  as  a  stained  specimen,  requires  considerable  time.  If,  e.  g., 
these  directions  are  given  in  the  Special  Technique,  "  Preserve  in  Miiller's  fluid 
fourteen  days,  harden  in  gradually  strengthened  alcohol,  color  the  section  in 
carmine  and  hsematoxylin,  mount  in  damar-varnish,"  then  the  proceeding  is  as 
follows  :  — 

The  fresh  specimen,  about  i  c.c.  in  size,  is  put  in  100  c.c.f  Miiller's 
fluid,  which  is  changed  as  soon  as  it  becomes  cloudy,  usually  in  one  hour 
(§4,  General  Rules).  In  twenty-four  hours  the  fluid  is  renewed,  and  in  this 
the  objects  then  remain  for  fourteen  days. 

At  the  expiration  of  this  time — 

JVash  in  (if  possible  running)  water  from  one  to  four  hours  ;   then 

Place  in  20  c.c.  distilled  water  fifteen  minutes;   next 

Place  in  50  c.c.  70  per  cent,  alcohol  twenty-four  hours,  in  the  dark  (see 
p.  29).      Next 

Place  in  50  c.c.  90  per  cent,  alcohol  twenty-four  hours,  and  then  transfer 
to  fresh  90  jier  cent,  alcohol. 

The  specimen  thus  fixed  and  hardened  can  be  cut  at  any  time.  The  sec- 
tions are  transferred  from  the  alcohol  (p.  30)  to — | 

*  The  oil  may  be  most  easily  and  successfully  removed  by  inclining  the  slide  as  one 
wipes  it. 

•f  The  quantities  of  the  different  fluids  are  reckoned  only  for  this  one  piece,  I  c.c.  in  size. 
For  several  pieces  or  larger  ones,  more  preserving  and  hardening  fluid  must  of  course  be  used. 

J  The  following  quantities  are  reckoned  for  3  to  6  sections.  With  more  sections  the 
amount  of  the  different  fluids  (of  absolute  alcohol  especially)  is  to  be  increased. 


THE    PREPARATION    OF    MICROSCOPICAL    SPECIMENS.  4I 

20  c.c.  weak  carmine  solution  for  twenty-four  hours  ;  then  to 

5  c.c.  distilled  water  for  about  ten  minutes.      Xe.xt  into 

5  c.c.  hsematoxylin  for  about  five  minutes, 
30  c.c.  distilled  water  for  from  ten  to  one  hundred  and  twenty  minutes, 

5  c.c.  absolute  alcohol  for  ten  minutes, 

3  c.c.  bergamot  oil  for  two  minutes,  and  finally  mounted  in  damar  varnish. 

§  II.   EXAMIN.-MION  OF  FRESH  OBJECTS. 

I  have  placed  this  method  last  because  it  is  the  most  difficult,  and  jjresup- 
poses  a  somewhat  practiced  eye.  Experience  is  gained  most  easily  by  exami- 
nation of  specimens  already  prepared  (hardened,  colored,  etc.).  If  one  has 
once  clearly  seen  and  studied  pecularities  of  structure,  then  it  is  not  so 
difficult  to  recognize  them  even  in  fresh  specimens,  though  most  of  the  details 
leave  much  to  be  desired  in  point  of  clearness.  The  following  directions  are 
to  be  observed  : — 

Slides  and  cover-glasses  must  not  be  oily.  They  should  be  cleaned  with 
alcohol  and  dried  with  a  clean  cloth.  Then  put  a  drop  of  0.75  per  cent. 
salt  solution  (p.  19)  on  the  slide,  and  in  it  place  a  small  piece  of  the  object  to  be 
examined,  and  cover  with  a  cover-glass.  The  slightest  pressure  must  be  care- 
fully avoided.  In  the  case  of  very  delicate  objects  (see  Special  Technique)  sup- 
port the  cover-glass  on  two  narrow  strips  of  paper  placed  one  on  either  side  of 
the  object.  If  the  specimen  requires  no  further  treatment  surround  the  cover- 
glass  with  paraffin  to  prevent  evaporation.  To  do  this  melt  a  small  piece 
of  paraffin  on  the  blade  of  an  old  scalpel  and  let  it  flow  from  this  on  the 
edge  of  the  cover-glass,  not  from  the  tip  but  from  the  edge  of  the  scalpel. 
In  most  cases  the  effect  of  certain  reagents  (acetic  acid,  potash-lye,  stains) 
on  fresh  objects  is  studied  directly  under  the  microscope.  It  is  then  necessary 
to  remove  a  part  of  the  medium  in  which  the  specimen  lies  (in  salt  solution 
in  the  present  instance),  and  to  replace  it  with  another  fluid.  For  this  purpose, 
first  place  a  drop,  e.  g.,  of  picrocarmine,  by  means  of  a  glass  rod,  at  the  right 
edge  of  the  cover-glass.  Should  the  drop  not  touch  the  edge  of  the  cover-glass, 
do  not  incline  the  slide,  but  lead  it  with  a  needle  to  the  desired  position.  One 
now  may  observe  that  a  little  of  the  stain  mixes  with  the  salt  solution,  but  does 
not  spread  out  under  the  glass.  To  make  the  latter  possible,  place  some  filter- 
paper  at  the  left  edge  of  the  cover-glass  *  and  at  once  the  picrocarmine  will 
diffiise  under  the  entire  surface  of  the  cover-glass. f  Now  remove  the  filter-paper 
and  let  the  stain  act.  When  the  staining  is  completed — this  is  to  be  ascertained 
under  the  microscope — place  at  the  right  edge  of  the  cover-glass  a  drop  of,  e.  g., 
diluted  glycerine,  to  which  is  added  (in  the  case  of  picrocarmine  staining)  as 


*  I  cut  a  piece  4  cm.  long,  2  cm.  broad,  fold  it  across,  and  place  the  paper  roof  thus  formed 
on  the  slide  in  such  a  way  that  one  smaller,  perfectly  straight  edge  touches  the  left  edge  of  the 
cover-glass. 

t  When  the  first  drop  has  penetrated  place  2  to  3  .idditional  drops  at  the  right  edge  of  the 
glass. 


42  HISTOLOGY. 

much  acetic  acid  as  will  drop  from  a  steel  needle  dipped  into  the  acid  (hence  a 
very  minute  drop),  while  the  filter  paper  is  again  applied  to  the  left  edge  of  the 
cover-glass.  In  this  way  a  whole  series  of  fluids  may  be  passed  through  beneath 
the  cover-glass  and  their  action  on  the  tissues  be  observed.  Certain  fluids, 
e.  g.,  picrocarmine,  must  remain  very  long  in  contact  with  specimens  previously 
fixed  in  osmic  acid.  In  this  case  evaporation  may  be  prevented  by  placing  the 
preparations  in  a  inoisi  chamber.  To  construct  the  latter  one  needs  a  porcelain 
plate  and  a  small  glass  bell  at  least  9  cm.  in  diameter'.  Into  the  plate  pour  water 
2  cm.  deep.  Then  place  in  the  middle  a  small  glass  dish  or  a  cork  plate  stand- 
ing on  four  wooden  feet.  On  this  the  slides  with  the  preparations  may  be  laid 
and  the  whole  covered  with  the  glass  bell,  the  free  edge  of  which  stands  in  the 
water. 

§  12.  STORIxN'G  OF  PERMANENT  SPECIMENS. 
The  mounted  specimens  must  be  labeled  at  once.  Cardboard  labels  i 
to  2  mm.  thick,  stuck  to  the  slide  with  fish-glue  ("isinglass")  are  preferable 
to  the  mucilaged  paper  ones,  for  such  mounted  slides  can  be  placed  upon  one 
another  without  pressing  the  specimens.  The  labels  should  be  as  large  as  pos- 
sible (2  cm.  square  for  slides  of  English  form)  and  should  have  designated 
upon  them  the  name  of  the  organ,  of  the  animal,  and  a  brief  indication  of  the 
methods  used.  For  boxes  and  cases  in  which  to  keep  the  specimens,  only 
those  in  which  the  slides  lie  horizontally  should  be  chosen,  and  not  those  in 
which  they  stand  on  edge.* 

*The  best  and  cheapest  cases  are  kept  by  Th.  Schroeter,  Leipzig,  Windmiihlenstr.,  No. 
46.  I  recommend  for  box  form,  patient  O  (for  about  300  slides),  price  2  M.  (50  cents) ;  for 
tray  form,  P,  with  flat  covers  for  lo  to  20  slides  (according  to  size),  price  45  Pfennige  (about  12 
cents).    The  tray  form  have  the  great  advantage  of  allowing  all  the  specimens  to  be  seen  at  once. 


III.  MANAGEMENT  OF  THE  MICROSCOPE. 

According  to  the  jiosition  taken  in  the  introduction,  an  exhaustive 
description  of  the  optical  and  mechanical  parts  of  the  microscope  cannot  be 
entered  upon  here.  Fig.  i  will  recall  to  the  reader  the  usual  names  of  the 
several  parts  of  the  microscope. 

The  first  requisite  in  the  use  of  the  microscope  is  perfect  cleanliness  of  all 
its  parts  (see  also  p.  17).  The  surfaces  of  the  mirror,  objectives,  and  oculars 
should  not  be  touched  with  the  fingers,  .\fter  the  ocular  has  been  placed  in 
the  upper  end  of  the  draw-tube,  and  a  low-power  objective  screwed  on  the 
lower  end  of  the  tube  (or  on  the  revolver,  if  used),  the  field  of  view  of  the 
microscope  should  be  illuminated  with  light  reflected  from  a  suitable  source  by 
the  concave  mirror  placed  below  the  stage.  This  is  best  accomplished  by 
moving  the  mirror  tentatively  in  all  directions  (with  the  diaphragm  widely 
open,  and  the  front  lens  of  the  objective  about  i  cm.  above  the  level  of  the 
stage)  till  the  eye,  looking  simultaneously  through  the  eye-piece  into  the  micro- 
scope, sees  the  field  of  view  brightly  and  uniformly  illuminated.*  Only  the 
concave  mirror  should  be  used  with  the  ordinary  objectives  recommended. 

The  best  light  for  microscopic  work  is  that  obtained  from  a  white  cloud, 
or  from  a  white  window-blind  illuminated  by  the  sun.  Of  less  value,  but  still  of 
use,  is  the  blue  sky.  Direct  sunlight  is  to  be  avoided.  Working  in  the  evening 
with  artificial  illumination,  light  from  the  inner  surface  of  a  white  lamp-shade 
(not  directly  from  the  flame)  should  be  used.  .\  plate  of  blue-gla.ss  placed 
before  the  mirror  renders  the  artificial  light  more  agreeable  to  the  eyes,  without 
blurring  the  outlines  of  the  picture  in  a  serious  degree.  It  is  obvious  that  the 
microscopist  should  not  sit  in  direct  sunlight.  The  instrument  should  be 
placed  about  a  meter  from  the  window. 

Now  the  examination  may  begin.  .Mways  examiney/Vj/  with  the  Itnc,  then 
with  the  hij^'h  power.  Avoid  especially  the  use  of  strong  oculars,  wliich  narrow 
and  darken  the  field  of  view,  and  thus  make  the  examination  much  more 
difficult.! 

*  The  rays  of  light  reflected  from  tlie  mirror  in  this  position  pass  peipendicularly  through 
the  object  on  the  stage.  This  is  called  central  illiiminalioti.  For  distinguishing  slight  differences 
of  level  between  adjacent  parts  of  an  object  it  is  of  advantage  to  use  oblique  or  lateral  illiimi- 
nalioii,  to  obtain  which  the  mirror  is  moved  to  the  side  so  that  the  rays  reflected  from  it  strike 
the  object  obliquely.  When  lateral  illumination  is  used  the  whole  diaphragm  should  be  taken 
away,  so  that  the  opening  in  the  stage  shall  be  as  large  as  possible. 

t  Nearly  all  the  preparations  used  for  the  ilUistraticm  of  this  book  were  e.xamined  and 
drawn  with  weak  oculars. 

43 


The  increased  magnification  obtained  by  drawing  out  the  draw-tube  is 
seldom  necessary.     With  low  powers  the  aperture  in  the  diaphragm  should  gen- 


Eye-piece  (Ocular) 


Draw-tube 


Triple  revolver 
Objective  ■ 


Eack  and  pinion  adjustment 


Micrometer  Screw 


Iri3  diaphragm 


Mirror 


erally  be  large,  with  high  powers  small.      In   focusing  the   object,  the  coarse 
adjustment  by  rack  and  pinion  is  used  first.     "With  its  aid  the  objective  is  first 


MANAGEMENT    OF    THE    MICROSCOPE.  45 

placed  at  a  distance  from  the  object  greater  than  its  focal  length,  and  then  with 
the  eye  applied  to  the  ocular  the  tube  is  gradually  lowered,  till  the  outlines  of  the 
preparation  appear  in  the  field  of  view.  The  image  is  then  brought  into  dis- 
tinct view  by  means  of  the  fine  adjustment  or  micrometer  screw.  In  doing  this 
the  left  hand  should  hold  the  slide,  while  the  right  remains  on  the  micrometer 
screw.  In  the  examination  of  the  preparation  the  tube  should  be  slightly  raised 
and  lowered  by  the  micrometer  screw,  because  only  the  points  lying  in  one 
plane  of  the  preparation  can  be  in  focus  and  distinctly  seen  at  one  time.  In 
using  the  microscope  the  habit  should  be  formed  of  keeping  both  eyes  open. 

One  should  never  neglect  to  examine  the  preparations  also  with  a  hand- 
lens.  For  this  purpose  the  oculars  {e.  g.,  Leitz,  Oc.  Ill)  can  be  used.  The 
mounted  specimen  is  held  with  the  cover-glass  side  toward  the  light.  The  upper 
lens  of  the  ocular  is  placed  directly  against  the  slide,  the  eye  apjilied  to  the 
lower  or  back-lens. 

DR.\\VIN(;. 
Drawing  is  a  very  valuable  aid  in  microscopical  work.  The  power  of 
observation  is  made  considerably  keener,  and  many  details,  which  would  be 
otherwise  completely  overlooked,  are  discovered  while  the  sketch  is  in  progress. 
Kven  the  most  attentive  examination  cannot  rejjlace  the  advantage  which  draw- 
ing yields.  Those  who  have  little  practice  in  drawing  should  nevertheless  try 
to  sketch  the  preparations  under  both  low  and  high  power.  For  this  purpose 
the  drawing  paper  should  be  on  a  level  with  the  stage,  the  left  eye  applied  to 
the  microscope,  the  right  directed  to  the  paper  and  the  pencil-point.  At  first 
this  is  rather  difficult,  but  a  little  i^ractice  will  soon  give  the  necessary  facility. 

ME.\SURE1SIENT. 
For  this  purpose  an  ocular-micrometer  and  stage-micrometer  are  used.* 
The  latter  is  laid  on  the  stage  and  focused,  and  the  number  of  divisions 
of  the  ocular-micrometer  which  corresponds  with  one  part  of  the  stage-micro- 
meter is  determined. t 

As  the  real  size  of  the  divisions  on  the  stage-micrometer  is  known,  it  is 
easy  to  determine  the  size  of  the  object,  which,  with  a  given  stage-  and  ocular- 
micrometer,  corresponds  with  one  or  more  divisions  of  the  ocular-micrometer. 
The  following  example  may  make  the  method  clear :   With  Leitz  Objective  3, 


*  Ocularniicrometers  are  in  some  c.nses  (Leitz)  made  to  simply  rest  upon  the  diaphragm 
inside  the  ocular ;  or  in  other  cases  (Seibert)  to  be  inserted  through  a  lateral  opening ;  in  others, 
again  (Zeiss),  specially  constructed  oculars  for  measuring  are  provided  for  the  microscope.  The 
real  size  of  the  divisions  of  the  ocular-micrometer  need  of  course  not  be  known.  The  stage- 
micrometer  is  a  glass-slide  on  which  a  millimeter  divided  into  100  parts  is  engraved.  Instead 
of  this  a  second  ocular-micrometer,  which  is  usually  divided  only  into  20ths  of  a  millimeter,  may 
be  used.  Measurements  made  with  this  are  naturally  not  so  accurate,  but  the  error  is  so  slight 
that  it  scarcely  need  be  considered. 

t  Heginners  often  have  trouble  to  focus  the  lines  of  the  stage-micrometer.  Weak  or 
oliliipie  illumination  makes  this  more  easy. 


46  HISTOLOGY. 

Ocular  I,  and  draw-tube  pushed  in,  5  divisions  of  the  ocular-micrometer  cor- 
respond with  I  division  of  the  stage-micrometer.  A  division  of  the  stage- 
micrometer  used  =  T^^  mm.  Hence  5  divisions  of  the  ocular-micrometer  = 
■^^  (0.05  mm.),  and  i  division  of  the  ocular-micrometer  =  0.0 1  mm.  If, 
then,  any  microscopic  object,  e.  g.,  a  striated  muscle-fibre,  the  diameter  of 
which  it  is  required  to  know,  occupies  4  divisions,  the  fibre  is  0.04  mm.  broad. 

It  is  often  difficult,  especially  with  low  magnification,  to  count  the  fine 
divisions  of  the  ocular-micrometer.  This  can  be  done  more  easily  by  taking 
advantage  of  the  longer  lines,  marking  every  fifth  or  tenth  division.  For  in- 
stance, with  LeitE  Objective  3,  Ocular  I,  and  the  draw-tube  drawn  out,  40 
divisions  of  the  ocular-micrometer  correspond  with  5  divisions  of  the  stage- 
micrometer.  Therefore,  40  divisions  =  y\  mm.  =  0.25  mm.,  and  one  division 
of  the  ocular-micrometer  with  this  magnification  =  0.0062  mm.,  2  divisions 
=  0.0124  mm.,  and  so  on. 

AVith  Leitz  Objective  7,  Ocular  I,  and  draw-tube  pushed  in,  30  divisions 
of  the  ocular-micrometer  correspond  with  i  division  of  the  stage-micrometer ; 
30  divisions  =  0.05  mm.,  i  division  =  0.0017  mm.,  or  7  //.  Finally,  with 
Leitz  Objective  7,  Ocular  I,  and  draw-tube  drawn  out,  40  divisions  of  the  ocu- 
lar-micrometer ^  I  division  of  the  stage-micrometer.  Therefore,  40  divisions 
=  0.05  mm.,  I  division  =  0.0012  mm.,  or  12  //. 

It  is  advisable,  if  one  has  many  microscopic  measurements  to  make,  to 
prepare  a  table  for  each  magnification  made  use  of,  in  which  the  real  values  of 
I,  2.  3  .  .  .  .  20,  30,  40  ...  .  100  scale  divisions  of  the  ocu- 
lar-micrometer are  given.  It  must  be  emphasized  that  the  examples  above 
given  by  no  means  apply  to  all  the  microscopes  made  by  Leitz.  The  values 
must  be  specially  determined  for  every  instrument  by  the  above  given  method. 

In  conclusion,  the  microscopist  is  e.xhorted  to  patience — great  patience  ! 
If  his  preparations  fail,  let  him  seek  the  cause  in  himself,  not  in  the  deficiency 
of  the  methods  recommended,  for  I  have  often  tested  them.  He  who  cannot 
accustom  himself  to  follow  out  conscientiously  the  directions  given,*  who  takes 
hold  of  delicate  objects  with  all  five  fingers,  who  contaminates  his  reagents  one 
with  another,  who  puts  his  specimens  in  their  fi.\ing  fluids  in  the  sun  or  lets 
them  dry  up,  is  not  justified  in  expecting  good  results  from  his  careless  work. 

*  The  lengths  of  time  given  for  staining,  dehydrating,  etc. ,  have  only  an  appro.vimate 
value.  They  vary  within  considerable  limits  in  accordance  with  the  thickness  of  the  sections, 
the  concentration  of  the  solutions,  etc.  Experience  will  soon  teach  the  microscopist  to  hit  the 
proper  time. 


PART    II. 

MICROSCOPICAL  ANATOMY. 

The  animal  body  is  composed  of  cells  which  are  all  produced  from  a 
single  cell  by  repeated  division.  At  the  beginning  of  development  the  cells 
are  of  like  form,  all  being  spherical,  and  none  is  furnished  with  special  charac- 
teristics to  distinguish  it  from  its  companions.  The  cells  are  still  undifferenti- 
ated. In  the  course  of  development,  the  cells  arrange  themselves  in  flat  super- 
posed layers,  the  so-called  genn-layers.  With  the  separation  in  germ-layers, 
and  with  the  formation  of  organs  from  these,  the  cells  cease  to  resemble  one 
another, — they  become  differentiated.  In  general,  the  cells  which  have  been 
differentiated  in  the  .same  direction  are  united  into  webs  or  complexes,  and  form 
a  tissue.  A  tissue,  therefore,  is  a  complex  of  similarly  differentiated  cells.  A\'e  dis- 
tinguish four  jirincipal  tissues  :  I.  Epithelial  tissue.  2.  Connective  tissue.  3. 
Muscular  tissue.  4.  Nervous  tissue.  So  long  as  these  tissues  are  still  young, 
they  are  composed  only  of  similar  elements,  of  cells ;  in  the  course  of  de- 
velopment, however,  this  condition  is  changed  in  a  two-fold  manner.  First, 
the  cells  produce  special  substances,  which,  being  deposited  between  them,  are 
called  intercellular  substances.  By  this  process  the  character  of  the  tissue, 
however,  is  not  essentially  altered.  The  definition  of  tissue  given  above  need 
only  be  so  far  e.xtended  that  we  call  a  tissue  a.  complex  of  similarly  differentiated 
cells  and  their  derivatives.  More  radical  is  the  second  change,  consisting  in  a 
penetration  of  tissues  of  one  kind  by  those  of  another.  The  extent  of  this 
change  varies  greatly  in  different  cases.  It  is  least  marked  in  the  case  of  the 
epithelial  tissues,  more  so  in  the  connective  tissues.  Muscular  and  nervous 
tissues  in  their  developed  forms  are  mixed  with  other  tissues  to  such  a  degree 
that  even  though  in  the  differentiated  elements  muscle  and  nerve  predominate, 
we  can  hardly,'  according  to  the  definition  given  above,  speak  of  the  structures 
as  "  tissues."  =*= 

The  tissues  are,  therefore,  not  e(|uivalent  among  themselves  as  regards  dif- 
ferentiation. Kpithelial  tissues  and  connective  tissues  stand  in  the  lowest  rank  j 
both  these,  differing  from  one  another  in  form  and  function,  occur  in  plants 
as  well  as  animals;  we  can,  therefore,  class  them  as  vegetative  tissues.  On  a 
higher  level,   both   morphologically  and  physiologically  stand  the  muscular 


*  For  this  reason  the  proposition  h.is  been  made  to  omit  a  division  of  tissues  and  to  dis- 
tinguish only  elements  and  organs. 

47 


46  HISTOLOGY. 

and   nervous  tissues,  which,  being  found  only  in  the  animal  body,  are  called 
animal  tissues. 

When  different  tissues  are  united  in  a  structure  of  definite  form  and  definite 
function,  they  constitute  an  organ.  Our  task,  therefore,  consists  in:  i,  the 
study  of  the  cells  and  of  the  tissues,  and,  2,  in  the  study  of  the  organs.  The 
investigation  of  cells  and  of  tissues  is  the  object  of  histology.  Histology  is  a 
part  of  general  anatomy,  which,  because  of  the  instrument  most  used  in  its 
study,  is  called  microscopic  anafo?ny.  The  investigation  of  organs,  also,  so  far 
as  it  can  be  done  with  the  aid  of  the  microscope,  is  the  task  of  microscopic 
anatomy. 


I.  HISTOLOGY. 

(^Aficroscopic  Anatomy  of  Cells  and  Tissues.) 
A.  CELLS. 

.\  cell,  cclliila,  is  a  structural  element  which,  under  certain  conditions,  is 
able  to  nourish  itself,  to  grow  and  to  multiply.  In  virtue  of  these  properties 
the  cell  is  called  an  elementary  organism. 

The  essential  parts  of  a  cell  are  :  i.  The  protoplasm,  or  cell-substance,  a 
soft,  semi-fluid  substance  of  alkaline  reaction,  insoluble  in  water,  highly  dis- 
tensible, consisting  principally  of  albuminous  substances,  much  water  and  salts, 
and  containing  a  special  nitrogenous  proteid,  plastin.  In  the  protoplasm  small 
granules,  microsomes,  occur  in  variable  numbers,  and  when  numerous,  give  to 
the  protoplasm  a  darker  appearance.  They  are  irregularly  distributed  ;  are 
absent  in  the  superficial  layer  (exoplasm),  which  is  somewhat  denser  and  per- 
haps possesses  a  special  function.  With  the  aid  of  very  high  magnifying  power 
it  will  be  seen  that  protoplasm  possesses  structure:  a  reticulum,  spongioplasm, 
which  is  embedded  in  an  amorphous  ground-substance,  hyaloplasm  (Flem- 
ming).*  2.  The  nucleits,  a  sharply  defined,  usually  vesicular  body  lying  in 
the  middle  of  the  cell,  and  consisting  of  several  proteid  substances,  chromatin 
(nuclein),  z.nA py renin  (paranuclein),  besides  linin,  the  fiuclear fluid  (matrix), 
and  amphipyrenin.  Both  chromatin  and  pyrenin,  by  their  affinity  for  stains, 
are  distinguished  from  the  other  three  so-called  achromatin  substances,  but 
differ  chemically  from  one  another.  For  example,  on  the  addition  of  dis- 
tilled water  the  structures  composed  of  chromatin  disappear,  while  those  com- 


*The  theories  concerning  the  structure  of  protoplasm  are  by  no  means  agreed.  Accord- 
ing to  Fromann,  Leydig,  and  others,  protoplasm  is  a  spongy  structure,  that  is,  it  consists  of 
a  network  whose  meshes  contain  a  fluid.  According  to  Butschli,  the  structure  is  froth-like,  that 
is,  it  contains  small  spaces  which  do  not  communicate  with  each  other.  According  to  the  much- 
disputed  theory  of  Altmann,  protoplasm  is  composed  of  granules  (granula,  bioplasts),  connected 
by  an  indifferent  substance,  and  these  are  the  real  elementary  organisms. 


CELLS.  49 

posed  of  pyrenin  remain  intact.  In  the  simplest  case  (in  spermatozoa),  the 
nucleus  is  a  compact  mass  of  chromatin,  to  which  the  pyrenin  is  attached,  but 
usually  it  is  composed  of  a  network  of  fine  linin  threads  and  of  coarser 
chromatin  cords.  *  The  chromatin  cords  are  of  different  caliber,  and  exhibit, 
at  intervals,  isolated  enlargements,  which  must  not  be  confused  with  the  nucleoli. 
Linin  and  chromatin  form  the  nuclear  network,  whose  interstices  are  occupied 
by  one  or  more  nucleoli  (consisting  of  pyrenin)  and  the  nuclear  fluid.  The 
nuclear  membrane,  not  always  present,  is  composed  of  amphipyrenin.  Often 
a  membrane  is  simulated  by  a  superficial  layer  of  chromatin.  The  nuclear 
network  and  nucleoli  undergo  important  changes  with  the  increasing  age  of 
the  cell. 

To  the  nucleus  belongs  the  centrosome,  a  minute  corpuscle  from  which  fine 
threads  e.xtend  to  the  chromatin  cords  and  to  the  nuclear  membrane.  Because 
of  its  minuteness  it  can  be  seen  only  in  particularly  favorable  objects  (in  the 


Niick-ir  fluid  (m.ilrix). 


Chromatin  cords  (nnck 
nelwork). 


Exopla 


Spongiopla 
Hyaloplasr 


--    Foreign  inclosu 
-Diagram  of  a  Crli..     Microsomes  and  spongioplasm  arc  only  partly  drawi 


spermatocytes  of  a.scaris  megalocephala  univalens,  in  carcinoma  cells),  and  then 
indistinctly,  until  it  wanders  from  the  nucleus  into  the  protoplasm,  which  it 
does  during  the  division  of  the  cell.  In  the  protoplasm  the  centrosome  can  be 
more  readily  seen,  and  seems  to  be  able  to  remain  there  for  a  considerable 
period.  There  it  was  first  discovered,  and  on  this  account  was  regarded, 
erroneously,  as  a  constituent  of  the  protoplasm  (Fig.  3). 

Most  cells  contain  but  one  nucleus ;  only  a  few  have  several  nuclei  (some 
wandering  cells,  giant  cells,  and  others).  Non-nucleated  cells  (horny  cells 
of  the  epidermis,  colored  blood-corpuscles  of  mammals)  originally  possess 
nuclei,  but  lose  them  in  the  course  of  development. 


*  In  certain  suitable  preparations  it  may  be  seen  that  the  chromatin  cords  are  composed  of 
rows  of  granules  which  lie  in  contact  with  threads  of  linin.  This  is  shown  in  the  upper  half 
of  the  diagram  (I'ig.  2). 


5° 


HISTOLOGY. 


An  unessential  element  of  the  cell  is  the  cell- membrane,  which  is  wanting 
in  many  cells,  and  when  present,  is  either  a  transformation  of  the  peripheral  zone 
of  the  protoplasm  or  a  secretory  product  of  the  latter.  It  appears  as  a  thin, 
usually  structureless,  membrane.  The  protoplasm  of  cells  may  contain  ad- 
ventitious materials,  pigment,  glycogen,  etc.,  and  globules  of  fat,  of  aqueous 
and  slimy  fluids.  The  term  paranucleus  (Nebenkern)  has  been  used  to 
designate  various  structures,  the  significance  of  which  is  not  yet  determined. 
A  paranucleus  is  often  simulated  by  the  remnants  of  degenerated  cells  which 
have  been  incorporated  in  a  living  cell.  In 
other  cases  the  paranucleus  is  confused  with 
the  centrosorae. 

Cells  differ  greatly  in  form.      They  may 

be :   spherical,  the  typical  form  of  all  cells  in 

s^  the  embryonal   period,  and  in  the  adult,  for 

"     Centrosome.  .  .... 

e.xample,  resting  leucocytes  are  spherical;  dis- 
oo.^'rhe' double  ''"'''.  <?•  S- ^  ^^  colored  blood -corpuscles; 
ear  area,  t  e  at-  polyhedral,  c.  g. ,  the  liver  cclls  ;  cylindrical  or 
columnar,  e.  g.,  the  epithelium  of  the  small 
intestine;  cubical,  e.  g.,  the  epithelium  of  the  capsule  of  the  crystalline  lens  ; 
flattened  (so-called  squamous  epithelium),  e.  g.,  the  epithelial  cells  of  the 
blood-vessels  ;  spindle-shaped,  e.  g.,  many  connective-tissue  cells  ;  elongated  into 
fibers,  e.g.,  smooth  muscle-fibers;  and  stellate,  e.  g. ,  many  ganglion-cells. 
The  form  of  the  nucleus  usually  corresponds  to  the  form  of  the  cell.  It  is 
more  or  less  oval  in  columnar,  spindle,  and  stellate  cells ;  rounded  in 
spherical  and   cubical  cells.     Lobulated,   so-called  polymorphous,  nuclei  are 


2/^ 


•Stef^ 


3/i         s         e  a         40  Minute 

Fig.  4. — Leucocytes  of  a  Frog.     X  560.    Changes  in  form  observed  during  t 


linutes.    Techn.  No.  43. 


found  in  leucocytes  and  in  giant  cells,  and  are  a  symptom  of  activity  on  the 
part  of  the  cell,  tending  either  to  locomotion  or  change  in  form,  or  to  increased 
metabolic  energy. 

The  size  of  cells  varies  from  forms  microscopically  small  (4  /i*)  (colored 
blood-corpuscles)  to  macroscopic  bodies  (eggs  of  birds,  amphibians).  The  size 
of  the  nucleus  corresponds  in  general  to  that  of  the  protoplasmic  body.  Only 
mature  ova,  despite  their  great  dimensions,  have  minute  nuclei. 


*  A  fUKpnv,  mikron  =  /i  =  o.ooi  mm. 


CELLS.  51 

The  vital  properties  of  cells  will  be  discussed  only  in  so  far  as  they  can  be 
studied  by  direct  microscopic  observation;  other  details  must  be  sought  in 
text-books  of  physiology.  Accordingly,  there  will  be  considered  here  the  phe- 
nomena of  motion  in  cells,  the  reproduction  of  cells,  and  those  microscopic 
processes  which  are  associated  with  the  secretory  activity  of  cells. 

"Wt  phenomena  of  motion  occur  in  the  form  of  amceboid*  activity,  of  cili- 
ary motion,  and  of  contraction  of  certain  fibers  (muscle-fibers).  The  amoeboid 
movement  is  the  most  important,  and  has  been  observed  in  nearly  all  the  cells 
of  the  animal  body.  In  especially  favorable  cases,  e.  g.,  in  leucocytes,  the 
protoplasm  of  the  cells  throws  out  finer  or  coarser  processes  ( pseudopodia;, 
which  by  dividing  and  flowing  together  produce  a  great  variety  of  forms.  These 
processes  may  retract,  or  they  may  become  fi.xed  and  draw  the  remainder  of 
the  cell-body  after  them,  the  result  of  which  is  locomotion,  or  the  so-called 
"  wandering  "  of  cells.  These  wandering  cells  play  an  important  part  in  the 
economy  of  the  animal  body.  The  proce.sses  can  flow  around  and  inclose 
foreign  particles  or  small  cells,  an  incident  described  as  the  feeding  of  the 
cell,  t  Amoeboid  movements  ensue  very  slowly;  in  warm-blooded  animals, 
only  on  artificial  warming  of  the  object.  For  ciliary  motion  and  contraction 
see  the  Epithelial  and  the  Muscular  Tissues. 

There  is  still  another  movement  which  is  observed  not  only  in  the  living 
but  also  in  the  dead  cell.  This  is  the  so-called  molecular  motion,  an  oscillation 
of  minute  granules  in  the  cell,  the  result  of  molecular  currents  in  the  fluid  in 
which  they  are  suspended.  It  may  often  be  observed  in  the  salivary  cor- 
puscles (.see  Lymph -follicles  of  the  Tongue). 

Reproduction  and  Multiplication  of  Cells. — Formerly,  two  kinds  of  cell  for- 
mation were  distinguished,  spontaneous  generation  {generatio  aquivoca')  and 
generation  by  division.  According  to  the  theory  of  spontaneous  generation, 
cells  originate  in  a  suitable  fluid,  cytoblastema.  This  view  has  been  utterly 
abandoned.  Only  one  kind  of  cell-generation  is  now  recognized ;  that  is,  re- 
production by  division  of  preexisting  cells,  "  Omnis  cellulse  cellula. "  ;j; 

In  the  division  of  a  cell,  first  the  nucleus  and  then  the  protoplasm,  divides 
into  two  usually  equal  parts.  In  this  process  a  special  grouping  and  rear- 
ranging of  the  nuclear  substances  take  place  according  to  definite  laws.  This 
mode  of  division  is  called  indirect  division,  mitosis,\^  karyokinesis.  Its  cycle 
is  usually  divided  into  three  phases,  as  follows: — 


*This  movement  is  exhibited  in  its  perfection  by  unicellular  organisms  named  amoeba;, — 
hence  the  phrase  "  amoeboid  movement." 

t  Not  to  be  confused  with  the  nutrition  of  the  cell,  which  is  effected  by  a  series  of  compli- 
cated chemical  processes  within  the  cells  ;  diosmotic  currents,  imbibition,  molecular  pressure,  etc. 

\  Likewise,  a  new  nucleus  can  be  formed  only  by  the  division  of  an  existing  nucleus. 
The  theory  of  spontanious  generation  of  nuclei,  according  to  which  nuclei  originate  directly  from 
the  protoplasm  and  independently  of  existing  nuclei,  lacks  convincing  evidence. 

11  /iiTOf  =  thread,  because  in  this  process  threads  are  visible  in  the  nucleus.  Tlitre  is 
a  second  mode  of  division,  in  which  the  nuclei  divide  simply  by  constriction,  without  a  deti- 
nite  grouping  of  the  nuclear   substances.     This  is   called  .//rc</  or  amitotic  division.     It  is, 


52 


HISTOLOGV. 


(i)  Prophase. — The  centrosome  increases  in  size  and  migrates  from  the 
nucleus  into  the  protoplasm.  There  it  lies  near  the  nuclear  membrane,  sur- 
rounded by  a  clear  zone  from  which  delicate  threads  radiate.  The  area  oc- 
cupied by  these  threads  is  called  the  attraction- sphere.  The  nucleus  enlarges  ; 
the  nuclear  network  becomes  richer  in  chromatin,  and  the  chromatin  cords 
assume  the  form  of  tortuous  segments,  chromosomes,*  transversely  disposed 
to  the  longitudinal  axis  of  the  nucleus,  and  the  number  of  which  is  constant 
for  each  animal  species.  The  form  of  these  segments  is  usually  that  of  a 
V-shaped  loop.  The  apices  or  closed  ends  of  the  loops  are  directed  toward  a 
common  center,  ^&  polar  field,— \\x.  area  in  which  the  centrosome  is  situated — 
their  free  ends  toward  the  opposite  pole  of  the  cell.  This  arrangement  of  the 
segments  is  called  the  close  skein.     It  is  followed  by  a  further  thickening  of 


Close  Skein  (viewed  Loose  Skein  (viewed  from  above, 

from  the  side),  i.  e.,  from  the  pole). 

Polar  field. 


Mother  Stars  (viewed  from  the  side). 


Mother  Star  (viewed 
from  above). 

Fig.  5.— Kabyoj 


■^^ii'^3?^ 


Division  of  the  ProtopI 


:iNETic  Figures  observed  in  the  Epithelium  of  the  Mouth  Ca 
n  the  upper  right-hand  corner  is  from  a  section  through  a  dividing  egg  of  Siredon  [ 
,  also  the  first  stages  of  the  development  of  the  spindle,  cannot  be  seen  by  this 
X  560.     Techn.  No,  16. 


the  segments  and  the  formation  of  the  loose  skein,  in  which  the  loops  are  less 
tortuous,  and  some  have  their  closed  ends  turned  away  from  the  polar  field. 


however,  very  probable  tliat  this  kind  of  tlivision  in  vertebrates  has  not  the  significance  of  a 
physiological  multiphcation  of  cells,  but  occurs  only  in  those  cells  which  are  on  the  point  of 
disintegrating,  for  very  often  the  division  of  the  protoplasm  does  not  follow,  so  that  only  a  mul- 
tiplication of  nuclei  takes  place.  This  frequently  happens  in  leucocytes,  also  in  epithelia,  e.  g. , 
in  the  superficial  epithelial  cells  of  the  bladder  of  young  animals. 

*  These  segments  are  present  also  in  many  resting  nuclei,  but  are  not  easy  to  distinguish 
because  of  the  many  lateral  branches  by  which  they  anastomose  with  their  fellows  to  form  a 
network.  When  the  process  of  division  begins  the  lateral  twigs  are  retracted,  and  con- 
sequently the  segments  become  thicker  and  more  conspicuous.  In  other  nuclei  the  chromatin 
appears  as  a  single  filament,  which  subsequently  divides  into  chromosomes. 


CELLS.  53 

Meanwhile  the  ceiitrosome  has  undergone  division  into  two,  each  sur- 
rounded by  an  attraction-sphere.  The  two  centrosomes  then  move  apart,  and 
the  interval  between  them  is  spanned  by  delicate  filirils,  which  form  the  central 
spindle.  This  soon  disappears.  The  centrosomes  continue  to  move  apart 
along  the  nuclear  membrane  through  an  arc  of  90  degrees.  The  threads  ex- 
tending from  the  centrosomes  to  the  chromosomes  persist.  Toward  the  com- 
pletion of  the  prophase  the  nuclear  membrane  vanishes  and  the  nucleolus 
becomes  invisible. 

(2)  Metaphase. — The  centrosomes  have  reached  diametrically  opjjosite 
points,*  and  the  threads  extending  from  them  to  the  chromosomes,  and  with 
which  parts  of  the  nuclear  membrane  may  be  a.ssociated,  now  appear  in  the 
figure  of  a  spindle,  the  nuclear  spindle.  At  each  apex  of  the  spindle  is  a  cen- 
trosome  surrounded  by  an  attraction-sphere,  which  in  this  stage  is  also  known 
as  the  "  polar  radiation."  The  chromatin  loops  move  to  the  equator  of  the 
spindle,  in  the  future  plane  of  division  of  the  nucleus,  and  arrange  themselves 
with  their  clo.sed  ends  directed  toward  the  axis  of  the  spindle.  Viewed  from 
the  apex  of  the  spindle  this  grouping  of  the  segments  has  the  appearance  of  a 
star,  mother- star  (monaster). 

During  the  formation  of  the  mother-star,  often  earlier,  in  the  first  stages 
of  the  prophase,  the  chromatin  loops  split  longitudinally,  and  each  forms 
two  "sister-loops."  Division  of  the  nucleus  exactly  into  halves  now  follows 
as  a  result  of  the  contraction  of  the  threads  of  the  spindle,  by  which  one  sister- 
loop  of  a  ])air  is  drawn  to  one  pole,  the  other  to  the  opposite  pole  of  the 
spindle.  This  is  called  metakinesis.  In  this  stage  the  nuclear  segments  ajjpear 
in  the  form  of  two  daughter-stars  (diaster). 

(3)  Anaphase. — These  figures  are  soon  obliterated.  The  lateral  twigs 
of  the  chromo.somes  reappear,  anastomose  with  one  another,  and  reproduce  the 
reticulum  of  the  resting  nucleus.  Meanwhile  the  spindle  has  become  invisible, 
and  also  the  greater  portion  of  the  polar  radiation,  the  nuclear  membrane  is 
reformed,  the  nucleus  reabsorbs  the  nuclear  fluid,  swells,  and  becomes  spherical, 
and  the  nucleolus  reappears.  .At  the  same  time  the  hitherto  quiescent  proto- 
plasm begins  to  divide,  a  furrow  appearing  at  the  equator  of  the  cell  and  deep- 
ening until  the  separation  into  two  halves  is  accomplished. 

In  rare  cases  of  mitotic  division,  especially  in  those  of  a  jiathologic 
nature,  the  nucleus  divides  simultaneously  into  more  than  two. 

The  duration  of  cell-division  varies  from  a  half  hour  (in  man)f  to  five 
hours  (in  amphibians). 

Special  modifications  of  cell-division  are  the  so-called  endogenous  cell- 
formation  and  budding.     The  former  occurs  in  those  cells  which  are  enveloped 


*  The  above  description  of  the  behavior  of  the  centrosomes  does  not  always  liold  good. 
For  example,  the  centrosome  in  Ascaris  megalocephala  univalens  divides  within  the  nucleus, 
which  elongates  and  extrudes  a  centrosome  at  each  end.  During  their  extrusion  the  nuclear 
spindle  is  formed.      In  succeeding  events  the  processes  are  identical. 

t  rhe  disappearance  of  the  mitotic  figures  in  the  human  cad.iveris  not  complete  until  after 
an  elapse  of  forty-eight  hours. 


54  HISTOLOGY. 

in  a  firm  capsule  (eggs,  cartilage  cells),  and  the  mode  of  division  is  precisely 
the  same  as  that  described  above,  only  that  all  the  descendants  of  the  mother- 
cell  remain  inclosed  in  the  common  capsule.  Gemmation  or  budding  indi- 
cates a  kind  of  unequal  cell-division,  in  which  protoplasmic  processes  of  the 
cell  are  set  free,  and  become  independent  cells  (as  in  bone-marrow). 

The  young  cells  always  resemble  in  character  the  mother-cells.  Such  a 
case  as  a  connective-tissue  cell  arising  from  the  division  of  an  epithelial  cell 
never  occurs. 

The  Phenomena  of  Secretion. — See  Secretory  Activity  of  Epithelial  Tissue. 

The  length  of  life  of  all  cells  is  limited.  The  old  elements  disintegrate, 
new  ones  appear  in  their  places.  Formerly  these  phenomena  were  not  distin- 
guished from  secretory  processes,  and  the  erroneous  idea  was  entertained  that 
the  process  of  secretion  terminated  in  the  death  of  the  cell.  Dying  cells  are 
characterized  by  decrease  in  the  volume  of  both  nucleus  and  protoplasm.  The 
latter  often  presents  a  notched  edge  or  stains  deeply,  while  the  chromatin  sub- 
stance of  the  nucleus  appears  either  shrunken  or  in  the  form  of  irregular  frag- 
ments that  react  alike  to  stains.  Vacuolization  of  the  protoplasm  or  the 
nucleus  is  another  symptom  of  degeneration. 

The  grmvth  of  cells  concerns  preeminently  the  protoplasm  and  only  ex- 
ceptionally takes  place  equally  in  all  directions,  in  which  case  the  original  form 
of  the  cell  is  retained  {e.  g.,  egg-cell)  ;  as  a  rule  an  unequal  growth  takes  place. 
As  a  result  of  unequal  growth  the  original  form  is  altered  ;  the  cell  becomes 
elongated,  or  flattened,  or  branched,  etc.  The  majority  of  cells  are  soft  and 
susceptible  to  change  in  form  from  mechanical  influences,  as,  for  example,  the 
coliuiinar  epithelial  cells  in  the  empty  bladder,  which  are  flattened  in  the  dis- 
tended organ. 

Secretory  Products  of  Cells. — The  secreted  materials  are  either  wholly 
removed  from  the  cells  (as  most  glandular  secretions)  or  they  harden  and 
remain  on  the  surface  of  the  cells.  To  the  latter  belong  certain  intercellular 
substances,  many  of  which  are  secretions  of  the  cells ;  others  are  produced  by 
change  in  the  peripheral  layers  of  the  cell-protoplasm,  still  others,  by  a  com- 
plete transformation  of  the  cells  themselves  (?).  It  is  very  difficult  to  decide 
whether  individual  intercellular  substances  were  formed  by  one  process  or 
another.      Many  points  in  this  matter  are  still  sharply  disputed. 

The  intercellular  substance  occurs  either  in  small  amount,  as  a  structure- 
less cement-substance,  found  between  epithelial  cells,  connective-tissue  cells, 
smooth  muscle-fiber,  etc.  ;  or  in  large  amounts  exceeding  the  mass  of  the  cells, 
and  is  then  called  matrix  or  ground-substance.  The  matrix  is  either  formless 
(homogeneous)  or  formed.  In  the  latter  case  it  consists  for  the  most  part  of 
fibers  or  granules  of  different  kinds.  The  remnants  of  formless  substance  found 
between  the  fibers  or  granules  are  also  called  cement-substance. 


55 


B.  TISSUES. 

I.  THE  EPITHELIAL  TISSUES. 

The  elements  of  epithelial  tissue,  the  epithelial  cells,  are  definitely  out- 
lined cells  consisting  of  protoplasm  and  a  nucleus.  A  cell-membrane  is 
frequently  absent,  or  is  represented  by  a  condensation  of  the  peripheral  zone 
of  protoplasm.  The  majority  of  epithelial  cells  are  soft  and  plastic,  and  yield 
readily  to  tlie  pres.sure  of  neighboring  cells,  the  result  of  which  is  great  diver- 
sity of  outline.  In  general  two  principal  forms  can  be  distinguished  :  the  Jlal- 
Uiuul  or  squamous  ?ind  Xht  cylindrical  or  eolumnar  (better,  prismatic).  These 
extremes  are  united  by  numerous  transitional  forms. 

The  scjuamous  epithelial  cells'are  seldom  regular  in  form,  excepting  the 
pigmented  epithelium  of  the  retina,  which  consists  of  tolerably  regular  hexa- 
gonal cells.      With  this  exception  the  outlines  are  usually  very  irregular. 


Fig.  6. — Epithblial  Cells  op  Rabbit,  Isolatbd.  X  560.  i.  Squamous  cells  (mucous  membrane  of  mouth), 
Techn  No.  85.  2.  Columnar  cells  (corneal  epithelium).  3.  Columnar  cells,  with  cuticular  border,  j  (intesti- 
nal epithelium).     4.  Ciliated  cells  :  h,  cilia  (bronchial  epithelium). 


The  cylindrical  oi)ithelial  cells,  cylinder  or  columnar  cells,  seen  from  the  side, 
are  elongated  elements  whose  height  considerably  exceeds  their  breadth,  and, 
seen  from  above,  appear  hexagonal  ;  they  are  therefore  in  reality  prismatic 
columns.      Cells  as  high  as  they  are  broad  are  called  cubical  epithelial  cells. 

[Since  any  form  of  epithelium  viewed  from  the  free  surface  may  present  a 
mosaic,  the  term  pavement  is  not  distinctive.] 

Many  columnar  cells  have  a  sometimes  homogeneous,  sometimes  striated, 
border  on  their  free  upper  surface,  the  cuticular  zone  (Fig.  6,  3.?). 

The  strife  are  the  optical  exi)ression  of  minute  rods,  occasionally  distinctly 
seen  even  with  medium  magnification  (Fig.  9  t")  ;  they  differ  greatly  in  length, 
and  answer  to  processes  of  the  protoplasm  that  penetrate  the  homogeneous 
zone.  To  the  same  category  belong  the  striations  seen  in  the  basal  half  of  the 
cells  lining  the  smaller  ducts  of  the  salivary  glands  and  some  of  the  tubules  of 
the  kidney.  The  latter  are  distinguished  by  their  greater  delicacy  and  their 
relation  to  secretory  activity  (they  have  been  seen  only  in  secreting  cells). 

Other  columnar  cells  are  beset  with  delicate  filamentous  processes  (cilia) 
on  their  free  surface,  which  during  life  are  in  constant  active  vibration  to  and 
fro  in  a  definite  direction.      These  are  called  ciliated  cells. 


56  HISTOLOGY. 

The  specially  differentiated  neuro-epithelial  cells  will  be  described  in  con- 
nection with  the  organs  of  special  sense. 

The  epithelial  cells  are  united  by  means  of  a  very  small  amount  of 
cement-substance,  and  present  either  smooth  surfaces  of  contact  to  one  another 
or  uneven  surfaces  and  an  interlocking  of  variously-shaped  processes, — the  pro- 
cesses being  pressure-effects — that  is,  the  result  of  the  mutual  pressure  of  con- 
tiguous cells. 

The  minute  spines  and  ridges  that  beset  the  surface  of  certain  epithelial 
cells  have  been  included  among  these  processes.  But  they  are  protoplasmic 
connecting  filaments  that  penetrate  the  cement-substance  and  establish  a  close 
internal  union  between  neighboring  cells.  Cells  furnished  with  such  spines 
and  ridges  are  called  prickle-cells,  and  the  processes  are  designated  intercellular 
bridges. 

Continuous  layers  of  epithelial  cells,  covering  outer  and  inner  surfaces  of 
the  body,  are  called  "  epithelia. "     The  epithelia  are  sometimes  com])osed  of  a 


Fig.  7.— From  a  Vertical  Sec-  Fig.  8.- 

TION  OF  THE  Stratum  Muco-  um    of    Retina    of    Man.  Epithelium  of  Intestine  of 

SUMOFTHE  F.plDERMis.  :■' 560.  V icvvcd  from  the  surfacc.  X  560.  Man.    X  =;6o.    c.  Striated  cuti- 

Seven   prickle-cells   united    by  Tcchn.  No.  170 .5.  cular  border.    =,  Columnar  cell, 

intercellular  bridges.      Techn.  /;*.     Tunica    propria.      Techn. 

like  No.  83.  like  No.  loj. 

single  stratum,  sometimes  of  several  strata,  and  accordingly  the  following  vari- 
eties are  distinguished  : — ■ 

1.  Simple  sqttamous  epitheliuiii :  in  the  outer  layer  of  the  retina,  in  the 
alveoli  of  the  lungs,  the  rete  vasculosum  Halleri,  the  membranous  labyrinth, 
the  choroid  plexuses  and  parts  of  the  ventricles  of  the  brain,  the  posterior  sur- 
face of  the  anterior  capsule  of  the  lens,  in  parts  of  the  ducts  of  glands,  and  in 
the  Malpighian  body  and  descending  limb  of  Henle's  loop  jn  the  kidney  ;  also 
in  the  peritoneum,  the  articular  cavities,  the  tendon-sheaths,  the  burs9e,  the 
blood-  and  lymph-vessels.  The  five  last  mentioned  epithelia  are  also  called 
ettdothelia — their  elements  endothelial  cells. 

2.  Simple  columnar  epithelium.:  in  the  intestinal  canal  and  in  the  ducts  of 
many  glands. 

3.  Simple  ciliated  epithelium  :  in  the  smallest  bronchi,  in  the  uterus  and 
oviducts,  in  the  accessory  spaces  of  the  nasal  fossae,  in  the  central  canal  of  the 
spinal  cord. 

4.  Stratified  squamous  epithelium  :  not  all  the  elements  of  which  are  flat- 
tened cells.  The  lowermost  stratum  is  composed  of  columnar  cells.  Super- 
posed  on   this  are  several  strata  of  variously-shaped   cells,  mainly  irregular 


TISSUES.  5  7 

polygonal  prickle-cells,  over  which  lie  successive  strata  of  cells  that,  as  they 
approach  the  surface,  become  gradually  thinner  and  flatter  (Fig.  lo).  The 
stratified  ])avement  epithelium  occurs  in  the  mouth  and  pharynx,  in  the  ceso- 
phagus,  on  the  vocal  cords,  on  the  cornea,  in  the  vagina,  and  in  the  female 
urethra.  The  epidermis  also  consists  of  a  stratified  pavement  epithelium,  but 
is  characterized  by  the  cornification  of  the  cells  of  the  superficial  strata,  which 
are  transformed  into  horny  scales  without  nuclei.  Cornified  cells  are  found 
also  on  the  hairs  and  nails,  but  in  these  situations  are  nucleated. 

5.  Stratified  columnar  epithelium,  in  man,  is  found  only  on  the  con- 
junctiva palpebrarum,  in  the  main  excretory  ducts  of  certain  glands,  and  in  a 
portion  of  the  male  urethra.  The  arrangement  of  tlie  strata  is  similar  to 
that  of — 

6.  Stratified  ciliated  efiithelium,  in  which  only  the  most  superficial  cells  are 
columnar  and  bear  cilia,  while  in  the  deepest  layers  the  elements  are  mainly 
spherical,  and  in  the  middle  layers,  spindle-shaped  (  Fig.  11).    Stratified  ciliated 


Squamous  Epithelium  (Lar-  Fig.   ii. — Stratified  Ciliated  Ei 

^   240.     I.  Columnar  cells.     2.  X  560.     From  ihe  respiratory  nasal  

Squamous  cells.      Tcchii.   No.  brane  of  man.     i.  Oval  cells.     2.  Spindle-shaped 

cells.     3.  Columnar  cells.    Techn.  No.  191. 

epithelium  is  found  in  the  larynx,  in  the  trachea,  in  the  larger  bronchi,  in  the 
na-sal  cavity,  in  the  upper  part  of  the  pharynx,  in  the  Eustachian  tube,  and  in 
the  epididymis. 

The  epithelium  has  no  blood-  and  lymph-vessels,  but  nerves  are  found  in 
some  situations,  for  example,  in  the  epithelium  of  the  skin  and  of  many  mucous 
membranes. 

Secretory  Activity  of  Epithelial  Tissue. — Many  epithelial  cells 
are  capable  of  secreting  and  discharging  certain  substances  which  are  not 
used  for  the  growth  and  development  of  the  tissue.  Such  cells  are  called  gland- 
ular cells.  The  secreted  substances  are  either  used  in  the  body  (secretions)  or, 
those  of  no  further  use,  removed  from  the  body  (excretions).  The  perform- 
ance of  the  processes  of  elaboration  and  discharge  of  secretions  (or  excretions) 
is  manifested  by  certain  changes  in  the  appearance  of  the  form  and  contents 


58  HISTOLOGV. 

of  glandular  cells,  and  which  indicate  conditions  of  rest  and  activity.  In 
many,  e.g.,  serous  glandular  cells,  the  differences  are  confined  (barring  cer- 
tain phenomena  in  the  nucleus)  to  decrease  in  volume  and  a  dark  appearance 
of  cells  empty  of  secretion,  and  to  increase  in  volume  and  a  clear  appearance 
of  those  filled  with  secretion.  In  other  gland-cells,  e.  g.,  in  many  mucous 
glands,  the  process  of  secretion  can  be  traced  more  accurately.  Granular 
protoplasmic  contents  and  a  usually  oval,  nearly  centrally  situated  nucleus 
indicate  a  condition  of  exhaustion.  The  elaboration  of  secretion  begins  at 
the  free  surface  of  the  cell,  that  directed  toward  the  lumen  of  the  gland,  and 
manifests  itself  by  the  transformation  of  the  granular  protoplasm  into  a  clear 
mass  (^b,  s),  more  or  less  sharply  defined  against  the  still  unaltered  protoplasm 
(J>,  p).  As  secretion  progresses,  more  and  more  of  the  protoplasm  is  trans- 
formed, and  the  nucleus  and  remnant  of  unaltered  protoplasm  are  pushed  to 
the  bottom  of  the  cell.  As  a  consequence  of  this  gradual  compression,  the 
nucleus  is  rounded  or  even  flattened.  The  volume  of  the  secreting  cell  when 
filled  is  considerably  enlarged.  Finally,  the  cell-wall  bursts  at  its  free  surface. 
The  secretion  gradually  escapes,  and  simultaneously  the  protoplasm  is  regen- 
erated, the  nucleus  moves  upward  to  its  original  position,  and  the  cell,  dim- 
inished in  size,  is  restored  to  its  previous  condition  and  appearance.     The 


'•'•-4-- 


Fig.  12. — Sbcrhting  Epithelial  Cells.  From  a  thin  section  of  mucous  membr.-tne  of  the  stomach  of  n 
X  5''0-  /■  ProtopKism.  s.  Secretion,  a.  Two  cells  empty  of  secretion:  the  cell  between  them  sh 
beginning  mucoid  metamorphosis,  c.  The  cell  on  the  right  is  discharging  its  contents,  its  upper  free 
having   ruptured;    the   granular    protoplasm   has    increased,    and   the   nucleus   has  become   round   ag 


majority  of  glandular  cells  do  not  degenerate  in  the  act  of  secreting,  but  are 
able  to  repeat  the  process  again  and  again.  The  cells  of  the  sebaceous  glands 
furnish  an  exception,  for,  like  the  goblet-cells,  their  secretion  is  formed  by 
the  disintegration  of  cells.*  In  the  case  of  the  latter  the  processes  of  elab- 
oration and  expulsion  of  the  secretion  occur  simultaneously ;  at  first  the 
secretion  is  produced  more  rapidly  than  it  is  discharged,  and  it  accumulates  in 
the  cell,  but  at  the  last  expulsion  exceeds  production,  the  cell  gradually  empties 
itself  completely,  and  dies  (Fig.  13). 

The  glandular  cells   lie  isolated  between  other  epithelial  cells  f   or  are 
united  in  groujis  and  form  glandular  tissue. 


*  The  testicle  and  ovary  furnish  a  peculiar  instance,  the  gland  cells  of  which,  after  secre- 
tion, undergo  further  development. 

t  They  are  then  called  unicellular  glands,  and  are  very  common  among  invertelirates,  but 
a]ipcar  also  in  man  as  goblet-cells. 


TISSUES.  59 

Supplement. — The  Glands. — The  glands  are  composed  almost  ex- 
clusively of  epithelium  fglandular),  and  therefore,  although  they  are  organs, 
they  may  be  described  with  the  epithelial  tissues.  Connective  tissue  and  blood- 
vessels are  present,  and  though  very  important  physiologically,  are  less  so 
morphologically. 

The  glands  occur  in  two  principal  forms  :  as  cylindrical  tubules  or  as 
rounded  saccules. 

The  tubular  glands  occur  either  singly  or  combined  into  groups ;  there- 
fore thev  are  divided  into — 


Secretion. 
Protoplasm  with  nucleus. 


GLind  lumen. 


3.    13. — CBVtT    OF    LlBBftRKi'-HN    FROM     A    Sf.CTION    OF    THR     LarGK     InTESTINH    OF     MaN.        X     165. 

secretion  formed  in  the  goblet-cells  is  dark  in  color.  In  zone  i  Ihc  goblet-cells  show  the  beginning  of  secre- 
tion. That  a  part  of  the  secretion  is  already  given  off  here  is  evident  from  the  presence  of  secretion  in  tht 
form  nf  drops  in  the  lumen  of  the  crypt.  2.  Goblet-cells  with  much  secretion.  3.  Cells  containing  a  smal 
amount  of  secretion.  4.  Degenerating  goblet-cells,  some  of  which  still  contain  remnants  of  secretion 
Tcchn.  10. 


The 


I.   Simple  tubular  glands,  which  have  the  form  of  simple  or  branched 
tubules  (Fig.  14)  ;  the  latter  may  be  called  a  "  duct-system."  * 


*  The  true  form  of  such  glands  can  be  recognized  only  on  the  most  exact  investigation, 
because  the  branched  tubules  are  twisted  about  one  another  or  coiled  in  a  dense  convolution. 
They  were  fonnerly  called  "racemose  glands." 


6o 


HISTOLOGY. 


2.   Compound  tubular  glands,  which  consist  of  a  large  and  variable  number 
of  "duct-systems"  (Fig.  14). 

The  same  division  is  applicable  to  alveolar  glands.      They  occur  as — 


Tiilnibr  Gland 


Simple  Glands.  Compound  Glands 

Saccular  (Alveol.-ir)  Glands. 


Terminal 

compartments. 


Simple  Glands, 
Fig.  14.— Diagram  o 


Saccules  (Alveoli). 


Compoimd  Glands. 
Different  Gland. Forms,    a.  Excretory  duct. 


I.  Simple  saceular  (^alveolar)  glands,  which,  similarly,  are  simple  or 
branched  saccules  having  an  excretory  duct ;  the  latter  are  termed  ''alveolar 
system." 


•  TISSUES.  6 1 

2.  Compound  saccular  {alveolar)  glands,  which  consist  of  a  combination 
of  several  "  alveolar  systems  "  (Fig.  14J. 

Simple  unbranchcd  tubular  s'ands:  the  peptic  or  fundus  glands,  the  sweat- 
glands,  and  the  glands  of  Lieberkiihn. 

Simple  branched  tubular  glands  :  the  pyloric  glands,  the  glands  of  Brunner, 
the  smallest  glands  of  the  oral  cavity,  the  glands  of  the  tongue,  and  the  glands  of 
the  uterus. 

Compound  tubular  glands  :  the  mammary,  the  salivary,  the  lacrymal  and  the 
larger  mucous  glands,*  the  kidneys,  the  glands  of  Cowper,  the  prostatic  glands, 
the  thyroid  gland,  the  testicle,  and  the  liver.  The  branches  in  the  last  two  anasto- 
mose and  form  networks,  and  hence  are  also  called  "reticular  glands." 

Simple  unbranched  saccular  glands:  the  smallest  sebaceous  glands  and  the 
follicles  of  the  ovary. 

Simple  branched  saccular  glands :  the  larger  sebaceous  glands  and  the  Meibo- 
mian glands. 

Compound  saccular  glands  :  the  lungs. 

In  the  majority  of  glands,  especially  in  those  visible  to  the  naked  eye,  a 
sheath  is  formed  by  the  surrounding  connective  tissue,  which  sends  septa  into 
the  gland  and  divides  it  into  compartments  of  varying  size,  the  gland  lobules. 
The  septa  carry  the  larger  blood-vessels  and  nerves.  The  glands  may  secrete 
throughout  their  entire  e.xtent,  but  usually  only  that  part  lying  near  the  blind 
end  {gland  follicle)  is  specialized  for  this  purpose,  while  the  part  forming  the 
connection  with  the  surface  serves  for  the  conveyance  of  the  secretion,  and  is 
called  excretory  duct. 

Glands  without  excretory  ducts  are  the  thyroid  body  and  the  ovary.  The 
former  has  an  excretory  duct  in  the  embryonic  period,  which  disappears,  how- 
ever, in  the  course  of  development.  The  gland  follicles  of  the  ovary,  in  the 
embryonic  period,  are  in  communication  with  the  sujierficial  epithelium;  these 
connections,  which  might  be  called  e.xcretory  ducts,  disappear,  and  the  expul- 
sion of  the  products  formed  in  the  ovary  (the  ova)  takes  place  by  the  bursting 
of  the  follicles.      The  ovary  is  a  dehiscent  gland. 

All  gland  follicles  are  composed  of  a  usually  simple  layer  of  gland  cells, 
which  bound  the  lumen  of  the  gland  and  are  in  turn  surrounded  by  a  special 
modification  of  the  connective  tissue,  a  membrana  propria  or  basement  mem- 
brane (see  p.  67).  Occasionally,  instead  of  this,  the  gland  tubules  are  em- 
braced by  stellate,  nucleated  cells  ("  basket-cells  ").     On  the  outer  side  of  the 

*The  cross-sections  of  the  coiled  and  closely-packed  branching  tubules  of  the  last  three 
glands  were  for  a  long  time  regarded  as  vesicular  evaginatioiis  of  the  terminal  ends  of  the 
tubules,  and  were  named  acini.  Such  evaginations  (except  in  a  few  isolated  parts  of  the  sub- 
lingual gland  do  not  really  occur;  the  diameter  of  the  lumen  is  not  larger  here  than  in  other 
portions  of  the  tubules.  Un  the  other  hand,  a  thickening  of  the  wall  of  terminal  parts  of 
tubules,  by  taller  cells,  is  not  uncommon  in  some  tubular  glands,  e.  g.,  in  the  parotid  and  the 
pancreas.  Such  thickenings,  however,  must  not  be  called  "  acini,"  since  we  understand  by 
acinus  an  evagination,  a  distention  of  the  lumen.  To  avoid  misunderstanding,  the  term  "aci- 
nus "  was  dropiwd  and  that  of  "  alveolus  "  selected  for  glands  of  the  saccular  form.  Likewise 
the  much-used  term  "acinous"  or  "racemose"  (alveolar)  has  been  discarded,  because  the 
cross-sections  of  lulmlar  glands  also  exhibit  a  "  racemose  "  appearance. 


62 


HISTOLOGY. 


basement  membrane  the  blood-vessels  are  situated  (Fig.  15).  The  gland-cells 
are  inserted  between  the  blood-vessels  and  the  lumen  of  the  gland,  and  on  the 
one  side  receive  from  the  blood-vessels  (or  the  surrounding  lymph-vessels) 
the  crude  materials  necessary  to  secretion,  and  on  the  other  side  give  off"  the 
elaborated  materials  as  secretion. 

In  some  glands,  e.  g.,  the  fundus  glands  of  the  stomach,  the  cell  dis- 
charges the  secretion  not  only  on  the  free  surface  but  on  all  sides.  The  secre- 
tion then  passes  into  a  network  of  canaliculi  that  envelopes  the  cell  and  com- 
municates with  the  lumen  by  a  single  wider  canal.  These  canaliculi  are  called 
secretory  capillaries. 

The  microscopic  appearance  of  the  gland-cells  changes  with  their  peri- 
odic functional  condition.  In  many  glands  all  the  cells  exhibit  simul- 
taneously the  same  functional  condition.  In  other  glands,  however,  dif- 
ferent functional  conditions  are  encountered  at  the  same  time,  even  within  the 


Mucous  Glands 
Blood-vessels  in- 
id-cells  were  only 
.     X  180.     Techn. 


Fig.  16. — Section  of  Fundus  Gland  op  Mouse. 
Left  upper  half  drawn  after  an  alcohol  preparation 
{Techn.  No.  102),  right  upper  half  after  a  Golgi 
preparation  (Techn.  No.  119).  The  entire  lower 
portion  is  a  diagrammatic  combination  of  both  prepa- 


same  tubule  or  alveolus.  The  latter  is  the  case  in  many  mucous  glands,  the 
cells  of  which  have  delicate  walls.  In  these,  cells  in  a  condition  of  activity  and 
of  exhaustion  are  found  side  by  side  in  the  same  tubule.  The  loaded  cells  push 
the  empty  ones  away  from  the  gland-lumen  ;  the  latter  then  lie  at  the  periphery 
of  the  tubule,  and  represent  in  this  form  the  so-called  "demilunes  of  Heiden- 
hain  "  or  "crescents  of  Giannuzzi"  (Fig.  17).  It  must  be  remarked  here 
that  other  authors  regard  the  crescentic  cells  as  young  gland-cells  destined  to 
replace  those  that  disintegrate  in  the  secretory  process.  The  absence  of  rem- 
nants of  disintegrated  cells  contradicts  this  interpretation,  as  does  also  the 
impossibility  of  demonstrating  karyokinetic  figures.  The  nuclei  of  many 
glandular  cells  also  exhibit  a  variable  appearance  according  to  the  functional 
condition.  In  an  empty  cell  the  nucleus  exhibits  a  delicate  chromatin  network 
and  a  conspicuous  nucleolus  (Fig.  17  /;),  while  in  loaded  cells  the  nucleolus  is 
invisible,  and  the  chromatin  network  appears  in  the  form  of  coarse  fragments 
(Fig.  17  «). 


TISSUES.  63 

The  smaller  branches  of  the  ducts  of  many  tubular  glands  must  be  regarded 
as  belonging  to  the  secretory  follicles,  since  they  are  characterized  by  the  spe- 
cialized epithelium  lining  their  walls,  and  participate  in  the  function  of  secre- 
tion by  eliminating  certain  materials  (salts).  They  are  thus  not  merely  excre- 
tory ducts,  but  belong  to  the  actively  secreting  portion  of  the  glands.  The 
difference  in  structure  of  these  branches  renders  their  division  into  two  parts 
desirable.  The  first  portion,  jiroceeding  from  the  terminal  compartments,  is 
narrow,  and  lined  sometimes  with  flat,  sometimes  with  cubical,  cells.  This  is 
called  the  infenalatcd  or  iiifermcdiatc  tubule.     The  adjoining  portion  is  wider 


Fig.  17.— Diagram  op  ti 

IB  Okigin  op  the  Crhschnts.     Protoplasm  shown  darkly 
shaded. 

shaded,  the  secretion  less 

I.   Cross-section    of  a 
tubule  of  a  mucous  gland, 
with  6  gland  cells.    3  («i. 
a.,  a.^)  are  filled  with  se- 
cretion, and  have  pressed 
the  three  cells  \hx,bz,b^ 

11.  Same  section  some- 
what later.  The  cells. ai. 
rt2>   "3)   liave    discharged 
a  part  of  their  secretion, 
and  become  smaller.  The 
ceils,    by.    I'a,    ^3,    again 

III.  Same  section  still 
later.     The  cells,  ay  a«, 
rt3,  have  discharged  the 
bulk    of    their  secretion, 
and  become  still  smaller. 
In  the  cells,  b^^b^,  ^3,  the 

IV.  Same  section  still 
later.     The  cells,  rtj,  do, 
«i3,  are  now  entirely  cm p"- 
ly,  and    pushed  entirely 
away  from  the  gland  lu- 
men by  bu  b..,  ba,  now 

empty  of  secretion,  away 
from    the   gland    lumen. 
Comp.  Fig.  146. 

extend  to  the  lumen  and 
begin  to  secrete. 

lated  to  such  an  extent 
that   they   have  become 
larger    and    compress 
tlicir   neighbors,   Uy,   flg, 

full  of  secretion. 

In  I  thecells/-,  inlV  the 

cells  a  are  the  crescents. 

and  clothed  with  tall  columnar  cells,  the  bases  of  which  show  distinct  longi- 
tudinal striation.  These  are  called  ititralohula?-  tubes  or  secretory  {salivary  or 
mucous)  tubes.  The  relative  length  of  the  intercalated  tubules  and  the  intra- 
lobular tubes  varies  greatly  in  the  different  glands. 

The  excretory  ducts  consist  of  a  simple  or  stratified  columnar  epithelium 
lining  a  wall  of  connective  ti.ssue  mingled  with  elastic  fibers. 

The  most  complex  glands  consist  of  the  following  sections  :  (i)  the  ex- 
cretory duct,  which  divides  into  (2)  the  secretory  tubes,  which  lead  into  (3) 
the  intercalated  tubules,  which  pass  into  (4)  the  terminal  compartments, 
which,  finally,  take  uj)  (5)  the  secretory  capillaries. 


64 


HISTOLOGY. 


II.   THE  CONNECTIVE  TISSUES. 

While  in  the  epithelial  tissues  the  cells  constitute  the  principal  mass,  in 
the  connective  substances  they  are  less  noticeable,  and  instead  the  intercellu- 
lar substance  is  conspicuously  develojied  and  variously  differentiated.  The 
predominance  of  the  intercellular  substance,  which  also  functionally  plays  the 
more  important  part,  is  characteristic  of  the  group  of  connective  tissues. 
According  to  the  nature  of  the  intercellular  substance  they  are  divided  into  : 
I.    Connective  tissue.      2.    Cartilage.      3.    Bone. 

I.  Connective  Tissue. — The  matri.x  or  intercellular  substance  of  con- 
nective tissue  is  more  or  less  soft ;  the  cells  are  few  in  number.  Several  varieties 
are  distinguished :  (a)  mucous  connective  tissue,  (^)  fibrillar  connective 
tissue,  and   {c)  reticular  connective  tissue. 

(a)  Mucous  connective  tissue  consists  of  round  or  stellate  branched  cells 
and  a  great  quantity  of  undifferentiated,  muciferous  intercellular  substance  con- 


^IG.  18. — From  a  Cross-Se 
Cord  of  a  Four  Months'  Human  Embryo.  X  240. 
I.  Cells.  2.  Intercellular  substance.  3.  Connec- 
tive-tissue bundles,  cut  obliquely,  but  at  4  directly 
cross-sectioned.     Techn,  No.  3. 


ivE-TissUE  Bundles  of  V 
FHE  Intermuscular  Conn 
X  240.     Techn.  No.  4. 


taining  a  few  minute  bundles  of  fine  fibrils.  In  the  higher  animals  it  is  found 
only  in  the  umbilical  cord  of  very  young  embryos,  but  is  very  common  in  many 
lower  animals. 

(J))  Fibrillar  (^areolar)  connective  tissue  consists  of  an  abundant  inter- 
cellular substance  and  cells. 

The  intercellular  substance  is  differentiated  into  connective-tissue  fibers, 
exquisitely  fine  (o.6/t)  filaments  united  by  a  small  quantity  of  homogeneous 
cement  into  bundles  of  varying  thickness — connective-tissue  bundles.  These 
bundles  are  soft,  flexible,  slightly  e.\tensible,  and  characterized  by  their  pale 
and  indistinct  contours,  their  longitudinal  striation,  their  wavy  course,  and 
also  by  their  chemical  properties.  On  treatment  with  picric  acid,  they  separate 
into  their  fibrils,  swell  up  on  the  addition  of  dilute  acids,  e.  g.,  acetic  acid, 
and  become  transparent.  They  are  destroyed  by  alkaline  fluids,  and  yield 
glutin  on  boiling. 


TISSUES.  65 

The  matrix  of  fibrillar  connective  tissue  always  contains  elastic  fibers,  but 
in  varying  quantities  (Fig.  20).  In  contrast  to  the  connective-tissue  bundles, 
they  are  characterized  by  their  shar])   dark  outlines,   their  strong   refractive 


'"^^'Q^^ 


Fig.  20.— Elastic  Fibfrs.    X  560-     A.  Fine  elastic  fibe 
connective-tissue   bundles   swelled  by  treatment   wit 
fibers,  y",  from  ligamentum  nuchae  of  ox  ;  b,  connective- 
section  of  the  ligamentum  nucha;  of  ox  ;  /,  clastic  fibe 


,  y,  from  intermuscul 


issue  of  man;  *, 

_jhn.  No.  10.    B.  Very  thick  elastic 

issue  bundles.     Techn.  No.  11.      C   From  a  cross- 
s;  b,  connective-tissue  bimdles.     Techn.  No.  12. 


power,  and  their  cons])icuous  resistance  to  acids  and  alkalies.  The  elastic  fibers 
vary  from  immeasurably  fine  to  ii  i>.,  and  occur  usually  in  the  form  of  finer  or 
coarser  networks,  the  meshes  of  which  are  sometimes  narrow,  sometimes 
large  (Fig.  21). 


Fig.  21.— Network  («)  of  thick  elastic  fibers, 
on  the  left  p:issing  into  a  fenestrated 'mem- 
brane (w/).  From  the  endocardium  of  man. 
X  560.     Techn.  No.  13. 


''        "-^K 


«i©    9  ;  ^  h 


Fig.  22  — A.  Connective>tissue  cells  from  intermuscular 
ncctive  tissue.  X  s6o.  i.  Flat  cell  lying  partly  on  a 
nective-tissue  bundle  :  2,  folded  cell :  3.  cell  of  whicl 
protoplasin    is    not_visible;    b,    connective-tissue    bundles. 


Techn.    No.    5.       B,    Coimective-tissue    bundle: 
circling   fibers:    *,   nucleus.      Techn.   No.   8.      C.  PI 
cells  from  the  eye-lid  of  a  child.     Techn.  No.  182 


th 


Narrow-meshed  networks  composed  of  thick  elastic  fibers  form  the  tran- 
sition to  elastic  membranes,  which  are  either  homogeneous  or  finely  .striated 
and  perforated  with  apertures  of  different  sizes  (hence  the  name  fenestrated 

5 


66 


membranes)  and  probably  are  produced  by  the  merging  of  broad  elastic  fibers 
(Fig.  2i). 

When  elastic  fibers  predominate  over  the  connective-tissue  bundles,  the 
tissue  is  spoken  of  as  elastic  tissue.  The  elastic  fibers  are  derived  neither  from 
cells  nor  from  nuclei,  but  are  a  transformation  of  the  matrix.  In  the  be- 
ginning of  their  development  they  are  thin,  but  thicken  in  the  progress  of 
their  growth. 

The  connective-tissue  cells  are  irregularly  polygonal  or  stellate,  flattened, 
and  variously  bent  or  folded  (Fig.  22,  A').  The  flattening  and  bending  are 
explained  by  the  adaptation  of  the  cells  to  the 
narrow  spaces  between  the  connective-tissue  bun- 
dles. Flattened  cells  not  infrequently  form 
sheaths  about  the  connective-tissue  bundles.  If 
such  a  bundle  be  treated, with  acetic  acid  it  swells 
and  bursts  the  ensheathing  cells,  of  which  encir- 
cling pieces  are  often  retained  and  constrict  the 
swelled  bundle.  Formerly  these  remnants  of  cells 
were  considered  fibers,  and  were  called  "encir- 
cling fibers"  (Fig.  22,  B').  Other  connective- 
tissue  cells  are  rounded,  rich  in  protoplasm, 
coarsely  granular,  and  comparatively  of  large  size. 
These  are  termed  plasma-cells,  and  are  found 
especially  in  the  neighborhood  of  small  blood- 
vessels (Fig.  22,  ^).  Others  again,  the  "  Mast- 
zellen, ' '  are  characterized  by  the  affinity  of  their 
protoplasm  for  certain  anilin  dyes  (<-.  ^g'.,  dahlia) 
but  do  not  stand,  as  their  name  might  suggest, 
in  any  demonstrable  relation  to  the  processes  of 
nutrition.  [They  are  also  known  as  granule- 
cells.'\  The  protoplasmic  body  of  the  connective- 
tissue  cells  encloses  a  nucleus  and  often  contains 
pigment-granules  ;  in  the  latter  case  they  are  called 
pigment-cells.  These  are  found  in  man  only  in 
certain  parts  of  the  skin  and  in  the  eye,  but  in 
the  lower  animals  they  are  very  common.  Con- 
nective-tissue cells  may  contain  fat-globules  which,  if  very  large,  coalesce 
and  give  a  spherical  form  to  the  cell,  which  is  then  designated  a  fat-cell 
(Fig.  23,  A').  In  such  cells  the  protoplasm  occupies  only  a  narrow  peripheral 
zone,  in  which  lies  the  extremely  flattened  nucleus.  This  protoplasmic  zone  is 
often  so  thin  as  to  be  invisible.  Aggregations  of  fat-cells  are  abundantly  sup- 
plied with  blood-  and  lymph-vessels  and  nerves,  and  form  what  is  called  adipose 
tissue,  which  bears  a  very  important  relation  to  metabolism.  In  cases  of 
extreme  emaciation  the  fat  in  fat-cells  is  reduced  to  a  few  small  globules.  In 
place  of  the  fat  which  has  disappeared  there  is  a  pale  protoplasm  mixed  with  a 
mucoid  fluid.      The  cell  is  no  longer  spherical,  but  has  become  flattened,  and 


Fig.  23. — Fat-Cblls  from  the  Ax- 
illa, /I,  OF  A  Lean  Individual. 
X  240.  I.  In  focusing  the  equator 
of  the  cell ;  2,  objective  somewhat 
elevated  ;  3,  4.  forms  changed  by 
pressure  ;  /.  traces  of  protoplasm 
in  the  vicinity  of  the  flat  nucleus,  k. 
B.  Of  an  emaciated  individual  ;  k, 
nucleus  ;  y",  fat-drops  ;  c ,  blood- 
capillaries, 
bundles.    Techn.  No.  9 


TISSUES.  67 

is  known  as  a  serous  fat-cell  (Fig.  23,  B).     In  many  fat-cells  after  death  spheri- 
cal masses  of  needle-shaped  crystals  appear — the  so-called  margarin  crystals. 

In  addition,  smaller  irregularly-spherical  cells  are  found  in  connective 
tissue  that  are  not  connective-tissue  elements,  but  leucocytes  that  have  passed 
out  of  the  blood-vessels.  They  are  described  as  "wandering  cells,"  in  dis- 
tinction to  those  of  the  connective  tissue,  which  are  designated  as  "fixed;  " 
but  this  cla,ssification  cannot  be  rigidly  carried  out,  since  in  certain  conditions 
(mainly  pathologic)  the  fixed  connective-tissue  cells,  and  also  epithelial  and 
glandular  cells,  can  migrate,  and  it  is  therefore  better  to  term  the  latter  "  his- 
togenetic,"  the  leucocytes  "  hematogenetic  "  wandering  cells. 

The  number  and  distribution  of  the  different  kinds  of  cells  is  subject  to 
considerable  fluctuation. 

The  different  elements  of  fibrous  connective  tissue  are  united  either  with- 
out any  definite  arrangement,  as  in  areolar  tissue,  or  are  regularly  disposed  in 
definite  structures.     Areolar  tissue 
is  distinguished  by  its  loosely-con- 
nected bundles  of  fibers  interlacing 

in    every    direction  ;     it    occurs    be-       Connective-tissue 

tween  neighboring  organs,  and 
serves  to  connect  them  and  fill  in 
the  interspaces.     For  this  reason  it 

'^  .  .  Network. 

is  also  called  "interstitial"  tissue. 
The  cells  of  areolar  tissue  not  in- 
frequently contain  fat.  The  fibrous 
connective  tissues  characterized  by  Leucocytes, 

closer  connection   and  regular  ar- 
rangement of  the  bundles  comprise  :       F.G.   24.-RETICULAR   CONNECTIVE   TISSUE.     From    a 
.1  ■  .1  t  shaken  section  of  a  human  lymph-gland.    X  560.   Techn. 

the  cormm,  the  serous  membranes,        no.  48.  j   f  b      .  ^  sou 

the  periosteum,  the  perichondrium, 

the  tendons,  fasciae,  and  ligaments  ;   the  compact  sheaths  of  the  central  nervous 
system,  of  the  blood-vessels,  of  the  eye,  and  of  many  glands. 

The  fibrous  connective  tissue  in  immediate  contact  with  epithelium  is  usu- 
ually  modified,  forming  a  structureless  membrane  called  basement-membrane  or 
membrana  propria,  also  hyaloid  membrane.  The  membrana  projiria  of  many 
glands — for  example,  salivary  glands — consists  of  basket-works  of  flattened, 
often  stellate,  cells,  which  surround  the  gland -tubules. 

{c)  Reticular  Connective  Tissue. — The  views  in  regard  to  the  structure  of 
reticular  connective  tissue  are  divided.  According  to  an  opinion  formerly 
widely  entertained,  it  consists  of  a  delicate  network  of  anastomosing  stellate 
cells,  and  to  this  may  be  traced  the  name  "  cytogenous,"  that  is,  formed  of 
cells.  Accordingly,  mucous  tissue  may  be  termed  cytogenous  tissue.  There 
is  no  doubt  but  that  such  networks  occur  in  lower  animals  and  in  embryonic 
stages  of  higher  animals.  In  the  higher  vertebrates,  however,  the  relations  are 
changed  ;  in  these  the  network  consists  of  slender  bundles  of  fibrillar  connective 
tissue,  upon  which  lie  flattened,  nucleated  cells  (Fig.  24).     By  means  of  com- 


68  HISTOLOGY. 

plicated  methods  the  outlines  of  the  cells  on  the  fibers  can  be  demonstrated. 
Finally,  the  fact  that  fibrillar  connective  tissue,  even  in  the  adult,  may  change 
into  reticular  tissue  can  only  be  comprehended  on  the  assumption  that  the  lat- 
ter is  a  network  of  delicate  fiber-bundles.  The  meshes  of  reticular  connective 
tissue  are  usually  crowded  with  leucocytes.  It  occurs  principally  in  lymph- 
glands  (better,  lymph-nodules),  and  is  then  called  adenoid  tissue. 

2.  Cartilage.— The  matrix  of  cartilage  is  dense,  elastic,  easily  cut,  and 
milk-white  or  yellowish  in  color.  The  cells  present  little  that  is  characteristic 
in  form ;  they  are  usually  spherical  or,  from  being  flattened  on  one  side,  some- 
what angular.  They  lie  in  the  spaces  or  lacuncB  of  the  matrix,  which  they 
fill  completely.  Whether,  as  in  bone,  the  matrix  is  penetrated  by  a  system  of 
minute  channels  communicating  with  and  connecting  the  lacunse  is  extremely 


6        ^ 


\l 


Fig.  25. — Hyalinf  Caki  il  \<,e.  X  240.  A.  Surface  view  of  the  ensiform  process  of  frog,  fresh;  /,  proto- 
plasm of  cartilage-cell,  which  entirely  fills  the  lacuna  ;  k,  nucleus  ;  g,  hyaline  matrix.  Techn.  No.  14.  B. 
Portion  of  cross-section  of  human  rib-cartilage  several  days  after  death  ;  examined  in  water:  the  protoplasm, 
2,  of  the  cartilage-cells  has  withdrawn  from  the  walls  of  the  lacimEe.A;  the  nuclei  are  invisible,  i.  Two 
cells  within  one  capsule,  k:  x,  a  developing  partition.  2.  Five  cartilage-ccUs  within  one  capsule  ;  the  low- 
est cell  has  fallen  out,  and  here  only  the  empty  space  is  seen.  3.  Capsule  cut  obliquely,  and  apparently 
thicker  on  one  side.  4.  Capsule  not  cut,  but  showing  the  cell  within,  g.  Hyaline  matrix  transformed  into 
rigid  fibers,,/".     Techn.  No.  15. 

doubtful.  Many  observations,  in  which  such  channels  were  apparently  seen, 
have  been  acknowledged  as  erroneous;  the  supposed  channels  were  a  result  of 
shrinkage,  and  can  be  produced  by  treating  cartilage  with  absolute  alcohol  or 
ether.  Not  infrequently  the  matrix  immediately  surrounding  the  lacunse  is 
specialized,  and  forms  a  strongly  refractive,  occasionally  concentrically-striated 
capsule.  The  otherwise  homogeneous  matrix  may  be  free  from  admixture  of 
fibrous  tissue,  or  it  may  be  penetrated  by  elastic  fibers  or  by  bundles  of  white 
fibers.  Accordingly,  three  varieties  are  distinguished  :  {a)  hyaline  cartilage, 
(d)  elastic  cartilage,  (r)  fibro-cartilage. 

(a)  Hyaline  cartilage  is  of  a  faint  bluish,  pearly,  transparent  color.  It 
occurs  as  the  cartilages  of  the  respiratory  organs  and  of  the  nose,  as  the  costal 
and  the  articular  cartilages,  also  in  the  synchondroses,  and   in  the  embryo  in 


TISSUES.  69 

many  situations  where  it  is  later  replaced  by  bone.  It  is  characterized  by  the 
homogeneity  of  its  matrix,  which  in  the  ordinary  methods  of  investigation 
appears  amorphous  throughout,  but  after  special  processes,  e.g.,  artificial  diges- 
tion, falls  apart  into  bundles  of  fibers.  Further  evidence  in  confirmation  of  its 
fibrillar  structure  is  afforded  by  its  appearance  when  examined  in  polarized  light. 
It  is  very  firm,  very  elastic,  and  on  boiling  yields  chondrin. 

In  certain  cases  the  matrix  may  undergo  a  peculiar  modification.  In  the 
thyroid  and  costal  cartilages  it  is  transformed  patchwise  into  rigid  fibers,  which 
impart  an  a.sbestos-like  lustre,  perceptible  on  macroscopic  inspection.  In  ad- 
vanced age  deposition  of  calcareous  salts  may  take  place  in  the  hyaline  matrix, 
in  the  beginning  appearing  in  the  form  of  minute  granules,  siib.sequently  as 
complete  husks,  surrounding  and  enclosing  the  cells.  In  the  cartilages  of  the 
larynx  this  may  occur  as  early  as  the  twentieth  year. 

The  cells  of  hyaline  cartilage  frequently  occur  in  groups  or  nests,  an 
arrangement  explained  by  the  conditions  and  processes  of  growth.  Two  cells 
may  lie  in  one  lacuna  and  be  enclosed  within  the  same  capsule  (Fig.  25,  £  i)  ; 


i^jmHi^lJim 


WL^ji  \'  !kk!\yjl 


Fig.  26. — Elastic  Cartilage.      X  240.     i-  Portion  of  section  of  vocal  process  (anterior 
cartilage  of  a  woman  thirty  years  old  ;  the  elastic  substance  in  the  form  of  granules, 
sections  of  epiglottis  of  a  woman  sixty  years  oltl  :  a  fine  network  of  elastic  fibers  in  : 
X.  Cartilage-celi,  nucleus  not  visible;  A,  capsule.     Techn.  No.  16. 


glc)  of  ar>'tel 

nd  ,.   Portion 

network  i 


they  are  the  descendants  of  the  original  cell,  which  has  undergone  division  by 
the  indirect  mode  ;  in  other  cases,  a  thin  partition  of  hyaline  substance  may 
be  seen  between  them.  In  still  other  cases,  the  septum  does  not  develop  im- 
mediately, and  the  process  of  cell-division  may  be  repeated,  until  groups  of 
four,  eight,  and  even  more  cells  may  be  enclosed  within  one  capsule  (Fig.  25, 
B  2~).  Such  phenomena  were  supposed  to  establish  a  special  theory  of  cell- 
division,  the  so-called  endogenous  cell-formation.  Not  infrequently  the  car- 
tilage-cells in  adults  contain  oil-globules. 

(J))  Elastic  cartilage  has  a  faint  yellowish  color.  It  occurs  as  the 
cartilages  of  the  external  ear,  of  the  epiglottis,  of  Wrisberg  and  Santorini, 
and  of  the  vocal  process  (anterior  angle)  of  the  arytenoid  cartilages.  It  pre- 
sents the  same  structural  peculiarities  as  hyaline  cartilage,  but  is  distinguished 
by  the  networks  of  finer  or  coarser  elastic  fibers  that  penetrate  the  matrix.  The 
elastic  fibers  do  not  arise  directly  from  the  cartilage-cells,  but  by  a  transforma- 
tion of  the  matrix,  and  appear  in  the  vicinity  of  the  former  as  minute  granules, 


70 


histolo(;y. 


J!l\ 


\ 


which  later  are  disposed  in  linear  rows  and  fuse  into  fibers.  This  phenomenon, 
according  to  an  opposite  view,  is  regarded  as  an  indication  of  post-mortem  dis- 
integration of  the  elastic  fibers. 

(f )  Fibro-cartilage  is  found  in  the  intervertebral  disks,  the  pubic  symphysis, 
the  inferior  maxillary  and  sterno-clavicular  articulations.  The  matrix  contains 
an  abundance  of  fibrous  connective  tissue  in  loose  bundles  extending  in  all 
directions  (Fig.  27,^).  The  cartilage-cells 
are  few  in  number,  have  thick  capsules,  and 
occur  in  small  groups  or  rows  at  com- 
paratively wide  intervals. 

3.  Bone. — -The  matrix  of  bone,  osse- 
ous tissue,  is  distinguished  by  its  hardness, 
solidity,  and  elasticity,  properties  due  to  an 
intimate  blending  of  organic  and  inorganic 
substances.  This  union  is  of  such  a  nature 
that  either  part  may  be  removed  without 
destroying  the  tissue.  On  treatment  with 
acids,  the  inorganic  substances  are  with- 
drawn ;  the  bone  is  decalcified,  is  rendered 
flexible,  and  is  easily  cut,  like  cartilage. 
On  the  other  hand,  the  organic  substances 
may  be  removed  by  cautious  heating  ;  the 
bone  is  tlien  said  to  be  calcined.  Fossil 
bones,  similarly,  are  deprived  of  the  organic  substances  through  the  prolonged 
action  of  moisture.  The  matrix  or  ground-substance  is  composed  of  calcium 
salts,  especially  basic  calcium  phosphate,  and  of  collagenous  fibrils,  united  by  a 


Fig.  27.^Fbom  a  Hori: 


Fibrilla 

r  connective  ti* 

isue; 

z.  cartilage-cell 

(nucleii 

s   invisible)  ;  k 

,  caps 

■ule  surroundeti 

by   calc 

lareous   granul< 

<   240.    Techn. 

'iG.  29. — From  Sections,  «,  of  the  Humerus  of  a 
Four  Months'  Human  Embryo  ;  h,  of  the  middle 
turbinal  bone  of  man ;  z,  bone-cells  lying  in  the 
lacunae,  h  ;  the  canalicuU  are  only  slightly  visible  ; 
g,  matrix.     X  560.     Techn.  No.  61. 


small  amount  of  cement-substance  in  finer  or  coarser  bundles  ;  accordingly,  a 
compact,  or  lamellar,  and  a  spongy  matrix  are  distinguished.  It  appears 
homogeneous  or  faintly  striated  and  contains  numerous  spindle-shaped  spaces 
15  to  27  //  in  length — the  lacuna' — from  which  minute  branched  channels — 
the  canaliciili — radiate  in  all  directions ;  the  lacunae,  with  their  minute  canals, 
form  an  intercommunicating  system  of  lymph-spaces  throughout  the  matrix. 
Within  the  lacunce,  sometimes  improperly  called  "bone-cells,"   lie  nucleated 


TISSUES.  7 1 

flattened  bodies,  the  real  hone-cells.  It  is  extremely  doubtful  whether  in  the 
adult  bone  the  cells  are  connected  by  means  of  jjrocesses  extending  through  the 
canaliculi,  although  such  connection  is  readily  observed  in  developing  bone. 

The  skeleton  of  the  adult  is  formed  principally  of  compact  bone,  which  is 
characterized  by  the  arrangement  of  the  fiber-bundles  in  lamellas  ;  the  matrix 
contains  elastic  fibers.  Spongy  bone  occurs  in  the  fetus  as  periosteal  and 
intermembranous  bone,  and  is  found  in  the  adult  along  sutures  and  at  the 
points  of  insertion  of  tendons  ;  it  always  contains  uncalcified  connective-tissue 
bundles,  the  so-called  Sharpey's  fibers,  which,  however,  are  also  found  in  the 
circumferential  and  interstitial  lamella;  of  compact  bone,  the  remains  of  the 
primary  or  periosteal  bone. 

Fibrous  connective  tissue  and  cartilage  may  be  converted  directly  into 
osseous  tissue  by  calcification  of  the  matrix ;  and  the  connective  tissue  and 


Bone-cell.    — 


Fic.  30. — Portion  of  Cross-Section  of  thb  Diaphysis  of  thb  Humerus  of  a  Four  Months'  H 


cartilage-cells  then  become  bone-cells.  This,  however,  is  of  comparatively 
rare  occurrence  ;  usually,  the  formation  of  osseous  ti.ssue  follows  the  calcifica- 
tion of  the  matrix  of  the  embryonal  cartilage  and  connective  tissue,  in  which 
young,  still  indifferent,  connective-tissue  cells  arrange  themselves  upon  the 
surface  of  the  calcified  trabecuhi;  and  produce  bone-substance. 

Dentine  is  a  modification  of  bone,  from  which  it  is  distinguished  by  its 
developmental  history  ;  the  formative  cells,  the  odontoblasts,  are  not  enclosed 
within  the  matrix,  but  penetrate  the  latter  with  their  processes.  Further  details 
will  be  found  in  connection  with  the  structure  of  teeth. 

Blood-vessels,  Lymphatics,  and  Nen'es. — Connective-tissue  structures  are, 
in  general,  poorly  supplied  with  blood-ves.sels,  lymph-vessels,  and  nerves.  An 
exception  occurs  in  adipose  tissue,  which  has  a  rich  vascular  supply.  Connec- 
tive tissue  plays  a  very  important  i)art,  however,  in  the  transference  of  nutritive 


72 


HISTOLOGY. 


fluids — tissue  jidics,  lymph — passing  from  the  blood-vessels  to  the  tissues.  When 
the  matrix  is  soft,  as  in  mucous  tissue,  the  lymph  permeates  the  entire  sub- 
stance ;  when  on  the  other  hand,  it  is  denser,  the  lymph  circulates  in  a  system 
of  intercommunicating  channels  formed  by  the  cell-spaces — lymph-spaces — and 
the  minute  canals  connecting  them — lymph-caiialiculi.  This  is  the  case  in 
bone  and  the  more  compact  connective  tissues.  Whether  the  tissue-juice  is 
diffused  throughout  the  matrix  of  hyaline  cartilage  or  conveyed  in  definite 
channels  is  still  undetermined.  The  intercellular  substance  of  epithelium  is  in 
direct  connection  with  the  lymph-capillaries  of  the  subjacent  connective-tissue, 
and  may  be  regarded  as  being  similarly  permeated  by  the  lymph. 

III.   THE  MUSCULAR  TISSUES. 

The  structural  elements  of  the  muscular  tissues,  the  inusclc-fibers.  occur  in 
two  forms,  the  smooth  and  the  striatcJ.  Both  are  cells  whose  body  is  extraor- 
dinarily elongated. 

I.  Smooth,  Non-striated,  or  Involuntary  Muscle. — This  consists  of  contrac- 
tile fiber-cells,  spindle-shaped,  cylindrical,  or  slightly-flattened  elements  with 
tapering  extremities  (Fig.  31).     They  vary  in   length  from   45  tq  225  //.  in 


G.  31.— Two  s 
potash-lye.     The 


I.     Isolated  with  35  per  t 
n  of  the  lye.     Techn.  No.  24 


width  from  4  to  1  jj.;  in  the  gravid  uterus  fibers  measuring  0.5  mm.  have  been 
found.  They  are  composed  of  homogeneous  protoplasm  and  an  elongated 
or  rod -shaped  nucleus ;  the  latter  is  characteristic  of  the  smooth  muscle- 
fiber.  The  protoplasm  of  certain  fibers,  those,  for  example,  of  the  vas 
deferens,  exhibits  longitudinal  striation,  which  has  led  some  authors  to  regard 
the  smooth  muscle-fiber  as  composed  of  minute  contractile  fibrillar.  In  fishes 
and  amphibians  muscle-fibers  containing  pigment  have  been  found  in  the  iris. 
[According  to  many  histologists  the  smooth  muscle-fiber  is  invested  by  an 
exceedingly  delicate  structureless  hyaline  sheath,  corresponding  to  the  sarco- 
lemma  of  the  striated  fiber.] 

The  fibers  are  collected  into  fasciculi,  and  firmly  held  together  by  a  homo- 
geneous cement-substance.  Communication  between  neighboring  fibers  by 
means  of  protoplasmic  processes  or  intercellular  bridges,  like  those  occurring 
in  certain  ephithelia,  has  been  observed  in  the  muscular  tunic  of  the  intestine 
of  the  dog  and  cat,  and  also  of  man.  Septa  of  connective  tissue  are  found 
only  at  comparatively  wide  intervals  (Fig.  32  ). 

The  fasciculi  are  united  to  form  strata  or  membranes,  in  which  their  dis- 
position is  parallel,  as  in  the  muscular  coat  of  the  intestine,  or  they  cross  and 
interlace  forming  complicated  networks,  as  in  the  urinary  bladder  and  the 
uterus.     The  larger  blood-vessels  run  in  tlie  connective-tissue  septa  ;  but  the 


TISSUES.  73 

capillaries  penetrate  the  fasciculi,  within  which  thev  Ibrm  networks  with  elonga- 
ted meshes.  The  lymph-vessels  follow  the  course  of  the  blood-vessels,  and 
are  present  in  considerable  numbers. 

For  the  nerves  of  smooth  muscle,  see  Peripheral  Nerve-endings. 

Smooth  muscle-tissue  occurs  in  the  alimentary  canal,  in  the  trachea  and 
bronchial  tubes,  in  the  gall-bladder,  in  the  capsule  and  pelvis  of  the  kidneys, 
in  the  ureters  and  the  urinary  bladder,  in  the  reproductive  organs,  in  the  vascu- 
lar channels  and  lymph -vessels,  in  the  eye,  and  in  the  skin.  The  contraction 
of  smooth  muscle-fiber  is  slow,  and  is  not  under  the  control  of  the  will. 

2.  Striated  or  Voluntary  Muscle. — It  is  only  by  the  study  of  their  develop- 
ment that  the  striated  muscle-fibers  can  be  recognized  as  the  morphologic 
equivalents  of  cells.  As  a  result  of  the  extraordinary  elongation  of  the  em- 
bryonal elements,  the  proliferation  of  their  nuclei,  and  the  peculiar  differentia- 
tion of  their  protoplasm  they  have  become  highly-specialized  structures.  The 
fibers  are  cylindrical  in  shape,  and  in  the  interior  of  the  larger  muscles  have 
rounded  or  pointed  ends  ;  on  the  other  hand,  at  the  extremities  of  the  muscle 
they  possess  a  pointed  inner  end,  while 
the  outer  end,  in  contact  with  the  tendon, 
is  broad.  The  latter  is  blunt  or  notched, 
often  step-like  and  tapering.  Anastomoses,  septun 
divisions,  and  fissures  occur;  branched 
fibers  are  found  in  the  muscles  of  the  eye, 
the  tongue,  and  the  skin  (Fig.  34,  4).  smooth^mulcie- 
They  vary  in  length  from  5.3  to  12.3  cm.,  «rsVs«"oT 

in  width  from  10  to  100  11.       It  is  probable       Fig.  32  -Srction  of  thb  Circular  Layer 
.\.^\  ri  -L       •  ..       1  ..1-  OF  THE  Muscular  Coat  of  the  Human 

that  there  are  fibers  having  greater  length.        Intestine,    x  560.   Tcchn.  No.  103. 
but  their  isolation  entire  is  very  difficult 

to  accomplish.  In  the  embryo  the  fibers  differ  but  little  in  width,  but  after 
birth  their  development  in  this  dimension  varies,  and  is  dependent  on  the 
functional  activity  of  the  muscle ;  in  the  adult,  robust  muscles  possess  thick 
fibers,  delicate  muscles  have  thin  fibers.  Apart  from  this,  their  diameter 
depends  also  on  the  nutritional  condition  of  the  individual.  Furthermore, 
larger  animals  possess  thicker  fillers  than  smaller  ones.  The  difference  in 
caliber  is,  therefore,  of  a  threefold  nature. 

Under  the  microscope  each  fiber  exhibits  alternate  broad  dim  and  narrower 
light  transverse  strife.  The  substance  of  the  dim  stripes  is  doubly  refracting  or 
anisotropic,  that  of  the  light  stripes  singly  refracting  or  isotropic.  High  amplifi- 
cation shows  that  both  the  dim  and  light  strise  are  transversely  divided  ;  in  the 
light  zone  a  delicate  dim  interrupted  line  may  be  seen,  the  intermediate  disk 
(Fig.  33,  q).  Each  part  of  the  light  zone,  above  or  below  the  intermediate  disk, 
constitutes  a  lateral  disk.  In  the  dim  transverse  band  a  clear  stripe,  the 
median  disk,  has  been  observed.  [In  certain  forms  of  invertebrate  muscles  the 
lateral  disk  is  crossed,  above  and  below  the  intermediate  disk,  by  a  dark  stripe, 
the  secondary  disk.']  Owing  to  their  extreme  variation  and  their  instability, 
these  disks  are  of  subordinate  significance.     Besides  the  cross-marking,  a  more 


74 


HISTOLOGY. 


or  less  distinct  longitudinal  striation  maybe  observed.  Treatment  with  chromic 
acid  solutions  renders  this  striation  more  evident,  and  may  even  effect  the  dis- 
integration of  the  fibers,  which  fall  apart  lengthwise  into  delicate  fibrils,  each 
of  which  exhibits  the  cross-striae.  These  fibrils  are  the  contractile  structural 
elements,  and  are  called  -ultimate  fibrilla. 

The  muscle-fibers  of  some  animals,  after  treatment  with  certain  reagents, 
cleave  transversely  into  disks.  Both  fibrillae  and  disks  may  be  further  separated 
into  smaller  prismatic  anisotropic  particles  called  sarcous  elements.  Certain 
authors  have  interpreted  the  disks,  others  the  sarcous  elements,  as  the  true 
structural  units. 

[According  to  the  theory  of  Rollett  regarding  the  structure  of  voluntary 
muscle,  the  fiber  is  composed  of  the  dim  anisotropic  contractile  substance  and 
the  light  isotropic,  relatively  passive  sarcoplasm.  The  highly-specialized  con- 
tractile substance  is  in  the  form  of  slender  spindles,  the  ends  of  which  are  pro- 
longed into  extremely  fine  filaments  and  terminate  in  a  minute  knob.      The 


spindles,  arranged  end  to  end,  form  the  continuous  contractile  fihrillce,  which 
grouped  in  parallel  bundles  constitute  the  sarcostyles,  and  extend  throughout 
the  length  of  the  fiber.  The  thicker  parts  of  the  apposed  spindles  form  the 
dim  transverse  bands,  the  knobs  the  dim  intermediate  disks  in  the  light  trans- 
verse bands.     The  spindles  correspond  to  the  sarcous  elements.] 

The  contractile  fibrillas  are  grouped  into  bundles — sarcostyles  or  viuscle- 
columns  ;  they  are  arranged  parallel  to  one  another  and  held  together  by  the 
sarcoplasm,  which  also  surrounds  and  unites  the  bundles.  The  disposition  of 
the  sarcoplasm  is  best  seen  in  cross-section  ;  high  amplification  is  required.  It 
presents  the  appearance  of  a  clear  network,  and  within  the  meshes  are  the 
muscle-columns  in  section, — small  dark  polygonal  areas  known  as  C(3/i///;d'/'w'i- 
yields.  The  sarcoplasm  contains  the  interstitial  granules — consisting  partly  of 
fat  and  probably  also  partly  of  lecithin — and  the  nuclei.  The  latter  are  oval 
bodies  placed  parallel  to  the  long  axis  of  the  fiber  ;  in  mammals,  bony  fishes, 
and  some  birds  they  are  chiefly  situated  immediately  beneatli  the  sarcolemma. 


TISSUES.  75 

upon  the  surface  of  the  muscle-substance ;  in  other  vertebrates  they  are 
embedded  within  the  sarcoplasni. 

Each  muscle-fiber  is  closely  invested  by  a  structureless  sheath,  the  sarco- 
lemma,  which  represents  the  cell-membrane.  Thus  the  fiber  of  striated 
muscle  comprises  the  fibrillar,  the  sarcoplasni,  the  muscle- nuclei,  and  the  sar- 
colemma. 

The  striated  fibers  are  found  in  the  muscles  of  the  trunk  and  the  extremi- 
ties, of  the  eye  and  the  ear,  also  in  the  tongue,  the  pharynx,  the  upper  half 
of  the  fjesophagus,  in  the  larynx  and  the  diaphragm,  the  genital  organs,  and  the 
rectum. 

In  some  animals,  the  rabbit,  for  example,  two  varieties  of  striated  muscles 
are  distinguished,  the  ?-ed  (semitendinosus,  soleus)  and  the  white  or  pale 
(adductor  magnus)  ;  and  correspondingly,  two  varieties  of  muscle-fibers:      i, 


Fig.  34. — Portions  op  IsoLATRD  Striated  MuscLB-FiBBRS  OF  Fkog.  X  50.  i.  After  treatment  with  water  : 
ji,  sarcolemma  ;  at  x  the  musclc-5:ubstance  is  torn  :  the  cross-striation  not  apparent,  the  longitudinal  striation 
distinct.  Techn.  No.  19.  2.  After  treatment  with  acetic  acid :  k,  nuclei :  the  minute  punctations  repre- 
sent interstitial  granules.  Techn.  No.  20.  3.  After  the  action  of  concentrated  potash  solution  ;  e,  rounded 
ends:  the  numerous  nuclei  are  swollen  and  vesicular  in  appearance.  With  tnis  amplification  the  cross- 
striation  in  a  and  3  is  not  visible.     Techn.  No.  32.     4.  Branched  muscle-5ber  from  the  tongue  of  the  frog. 


dim  fibers,  rich  in  sarcoplasni,  less  regularly  cross-striped,  exhibiting  distinct 
longitudinal  striation,  and  possessing  in  general  a  smaller  diameter  (found  in 
the  soleus  of  the  rabbit)  ;  2,  pale  fibers,  poor  in  protoplasm,  more  distinctly 
cross-striated,  and  having  in  general  a  greater  diameter.  The  latter  represent 
the  more  highly-differentiated  fibers.  While  in  certain  animals  the  two  varie- 
ties of  fibers  occur  separately,  each  in  particular  muscles,  in  others — also  in 
man — they  are  found  intermingled  in  the  same  muscle.  As  a  rule,  the  more 
functionally  active  muscles — cardiac,  ocular,  masticatory,  and  respiratory — 
contain  the  greater  number  of  red  fibers.  The  pale  fibers,  on  the  other  hand, 
respond  more  rapidly  to  electric  stimulation. 

The  contraction  of  the  striated  fibers,  as  compared  with  that  of  smooth 
muscle,  is  quick,  and  is  under  the  control  of  the  will.  The  striated  fibers  are 
united  into  bundles  by  areolar  tissue,  which  serves  also  to  convey  the  numer- 


76 


HISTOLOGY. 


ous  ramifications  of  the  blood-vessels  and  nerves  supplying  the  muscular  tissue. 
The  lymphatic  vessels  are  few  in  number. 

3.  Cardiac  Muscle. — The  muscle-fibers  of  the  heart  occupy  a  peculiar 
position.  Although  transversely  striated,  in  the  history  of  their  development, 
as  well  as  histologically,  they  must  be  regarded  as  modifications  of  the  smooth 
muscle-fibers.  In  the  lower  vertebrates,  in  frogs  for  example,  they  are  spindle- 
shaped,  possess  elongated  nuclei,  and  are  often  more  distinctly  striated  trans- 
versely than  longitudinally  (Fig.  35,  A'). 

The  cardiac  muscle  of  mammals  consists  of  short,  cylindrical  fibers,  the 
ends  of  which  are  often  step-like.  The  protoplasm  is  partially  differentiated 
into  cross-striated  fib)illcz,  which  not  infrequently  are  grouped  into  muscle- 
columns  radially  arranged  to  the  axis  of  the  fiber  (Fig.  35,  Z>).  The 
remnant  of  undifferentiated  protoplasm — sarcoplasm — proportionately  consid- 


~ffl 


C 


,<y 


Fig.  35.—^  and  B,  Muscle-Fibeks  of  Heart,  isolated  in  potash-lye.  A.  Of  frog.  £.  Of  rabbit :  .r,  lateral 
branches.  X  240.  Techn.  lilie  No.  22.  C.  In  longitudinal  section.  D.  From  a  cross-section  of  papillary 
muscle  of  man.     C  magnified  240, /),  560  diameters.     Techn.  No.  33. 


erable  in  comparison  with  that  of  striated  voluntary  fibers,  is  found  chiefly  in 
the  axial  part  of  the  fiber,  from  which  jsrocesses  radiate  between  the  muscle- 
columns.  Longitudinal  striation  is  often  marked,  owing  to  the  generous 
amount  and  the  disposition  of  the  sarcoplasm.  The  oval  nucleus  is  embedded 
in  the  axial  part  of  the  sarcoplasm,  which  frequently  contains  pigment-granules 
or  oil-droplets.  A  cell-membrane  or  sarcolemma  is  wanting.  The  cardiac 
muscle  of  the  higher  animals  is  characterized  by  the  anastomosis  of  the  cells 
by  means  of  short,  lateral  processes.  [The  cells  are  joined  end  to  end,  trans- 
verse lines  of  cement-substance  indicating  the  line  of  union  between  the 
individual  elements.] 


IV.  THE  NERVOUS  TISSUES. 

The  elements  of  the  nervous    tissues  in   an  early  embryonic  stage  are, 

without  exception,  cells  having  a  spherical  form ;  they  are  called  tieuroblasts. 

In  the  course  of  their  development  they  become  elongated  and  pyriform,  and 

the  narrow  end  grows  out  as  a  long,   delicate  process  (nerve- process),  often 


77 


Nerve-process. 


Mcdullarj'  sheath. 


■"  Neurilemma. 


extending  to  the  length  of  a  meter;  it  terminates  in  a  free  branched  end,  and 
is  named  axis-cylinder  process.  From 
the  body  of  the  cell — now  termed  a 
nerve-  or  ganglion-cell — other  pro- 
cesses may  arise,  which,  however, 
are  short  and  divide  dichotomously  ; 
these  are  called  protoplasmic  or  rami- 
fying processes  (dendrites).  The  axis- 
cylinder  process  also  may  have  delicate 
lateral  branches,  the  collateral  fibrils. 
The  nerve-cell  and  axis-cylinder  pro- 
cess together  constitute  the  neuron; 
the  dendrites  and  collateral  fibrils  may 
be  regarded  as  secondary  processes  of 
the  neuron,  forming  with  the  latter  the 
neurodendron. 

The  axis-cylinder  process  may  be 
naked  throughout  its  extent,  or  it 
may  be  invested  by  different  sheaths  ; 
these  are  the  neurilemma,  or  sheath 
of  Schwann,  and  the  medullary  sheath, 
or  white  substance  of  Schwann. 
Both,  originally  alien  to  the  nervous 
tissues,  are  derived  from  connective 
tissue ;  both  invest  the  axis-cylinder 
only  in  a  portion  of  its  course. 
There  are  stretches  in  which  the  axis- 
cylinder  is  entirely  without  invest- 
ment, is  naked  (Fig.  36,  a)  ;  stretches 
in  which  it  is  enveloped  by  either  the 
neurilemma  (Fig.  36,  b")  or  the  medul- 
lary substance  (Fig.  36,  c'),  and, 
finally,  stretches  in  which  both  sheaths 
are  present  (Fig.  36,  </)  ;  in  the  latter 
case  the  medullary  sheath  is  always 
the  innermost  envelope,  lying  directly 
upon  the  axis-cylinder,  and  is  itself 
ensheathed  by  the  neurilemma.  The 
axis-cylinder  always  occupies  the 
longitudinal  axis,  hence  its  name. 
Owing  to  the  often  great  length  of  the 
axis-cylinder,'  it  is  not  possible  to 
investigate  the  neuron  as  -a  whole. 
.\s  a  rule,  it  is  seen  only  in  fragments,  either  the  nerve-cell  or  the  axis-cylinder, 
and  this  explains  the  former  division  of  the  elements  of  the  nervous  tissues  into 


\, 


Fic.  36.— Diagram  of  a  Nbukon. 


78 


HISTOLOGY. 


nerve-cells  and  nen'e-fibers — the  latter  being  the  axis-cylinder  processes  with 
their  sheaths.  There  are  no  independent  nerve-fibers,  each  so-called  fiber 
is  a  process  of  a  ganglion-cell.  However,  for  practical  reasons,  the  old  classi- 
fication is  retained. 


Nerve-Cells. 
Nerve,  or  ganglion-cells,  are  found  in  the  ganglia,  in  the  organs  of  special 
sense,  along  the  course  of  cerebro-spinal,  as  well  as  sympathetic  nerves,  but 
principally  in  the  central  nervous  system.  They  differ  greatly  in  size  (4  to 
135  /jt  and  more)  and  in  form.  There  are  spherical  and  spindle-shaped  ganglion- 
cells,  and  irregularly-stellate  forms  are  very  common  ;  the  latter  are  those  in 
which  the  protoplasm  sends  off  numbers  of  processes  and  so  gives  rise  to  the 
stellate  outlines.      Ganglion-cells   having   two   processes  are  termed   bipolar, 

those  having  several  processes,  multipolar 
ganglion-cells  (Fig.  37).  There  are 
also  unipolar  ganglion  cells  ;  these  occur 
in  the  sympathetic  nerve  of  amphibians 
and  universally  in  the  olfactory  mucous 
membrane.  They  possess,  in  fact,  but 
a  single  process.  The  nerve-cells  of  the 
spinal  ganglia,  on  the  other  hand,  are 
only  apparently  unipolar  ;  bipolar  in  the 
embryo,  in  the  course  of  development 
they  become  unipolar  by  the  gradual 
approach  of  the  processes,  which  event- 
ually come  off  from  the  cell  by  a  com- 
mon stalk,  from  which  they  then  diverge 
at  right  or  obtuse  angles.  These  are  the 
cells  described  as  having  T-shaped  or 
Y-shaped  processes.  Apolar  cells,  that 
is,  ganglion -cells  without  processes,  are 
either  immature  forms  or  artificial  products,  the  processes  in  the  latter  case 
having  been  torn  off  in  the  manipulation  required  for  isolation. 

The  ganglion-cells  are  composed  of  granular  or  finely-striated  protoplasm 
and  have  a  characteristic  vesicular  nucleus,  poor  in  chromatin  and  enclosing  a 
conspicuous  nucleolus.  The  protoplasm  not  infrequently  contains  yellowish- 
brown  pigment-granules  (Fig.  37).      A  cell-membrane  is  wanting. 

The  processes  of  nerve-cells  are  of  two  kinds  :  i,  the  axis-cylinder  (Deit- 
ers's)  and,  2,  the  branched  protoplasmic  processes  (Fig.  38).  They  are  most 
readily  distinguished  in  the  multipolar  cells.  The  axis-cylinder — usually  the 
only  process  of  the  kind — is  the  first  outgrowth  from  the  embryonal  spherical 
cell,  and  is  characterized  by  its  hyaline  appearance  and  smooth  outlines ;  its 
course  is  cellulifugal — it  leads  from  the  cell.  Tlje  protoplasmic  processes — 
usually  several  in  number — are  a  later  outgrowth  of  the  embryonal  cell,  are 
thicker,  granular  or  finely  striated,  and  often  varicose  ;   their  course  is  cellu- 


FiG.  37.-V 
X  240-  I 
ticum  of  ; 
Muttipolai 
Techn.   No 


Rious  Foii\ 

Bipolar  cell  from  the  ganglion  a 

I  embryo  rat.     Techn.  No.   187 

from   the   spinal   cord  of  i 

Cell    fron      '       - 


on  of  man,  axis-cylinder  process  torn  off. 
Fin.  No.  25.  4.  Cell  with  T-branches  from  a 
al  ganglion  of  a  young  rat.     Techn.  No.  70. 


TISSUES.  79 

lipetal — toward  the  cell.  They  undergo  repeated  dichotomous  division  and 
terminate  in  an  intricate  network  of  extremely  fine  fibrils.  Cells  possessing 
more  than  one  axis-cylinder  process  occur  in  the  brain  of  the  rabbit,  in  the 
substantia  gelatinosa  of  the  spinal  cord  of  the  chick,  and  perhaps,  also,  in  the 
sympathetic  nerves  of  the  higher  vertebrates.  In  bipolar  cells  (si)inal  gang- 
lion-cells of  the  lower  vertebrates  and  embryos)  in  which  both  processes  be- 
come the  axis-cylinders  of  medullated  nerve-fibers,  the  fiber  going  toward  the 
central  nervous  system  corresponds  to  the  axis-cylinder  process,  the  peri- 
pheral fiber  to  a  jjrotoplasmic  jirocess. 


Axis-cylinder  process. 


Fig.  38. — Nhkve-Cell  (Cell  op  Pukkinjb)  from  a  Section  thkough  the  Hi'man  Chkebellar  Co 
X  180.     Techn.  No.  74. 


Dependent  on  the  behavior  of  the  axis-cylinder  process,  two  kinds  of 
ganglion-cells  are  distinguished — cells  of  the  first  type,  having  a' long  axis- 
cylinder  process  which  becomes  the  axis-cylinder  of  a  medullated  nerve-fiber, 
and  cells  of  the  second  type,  having  a  short  axis-cylinder  process  which  divides 
and  subdivides  and  terminates  in  a  nervous  ramification  in  the  vicinity  of  the 
cell  (Fig.  39).  The  axis-cylinder  process  of  cells  of  the  first  type,  after  giving 
off  a  number  of  fine  branched  twigs,  the  collateral  fibrils,  and  running  an 
extended  course,  often  embracing  many  centimeters,  as  the  axis-cylinder  of  a 


8o 


HISTOLOGY. 


nerve-fiber,  undergoes  rapid  division  and  terminates  in  a  plexus  of  delicate 
fibrils.  All  the  processes  terminate  in  free  endings,  without  forming  anasto- 
moses ;  there  is  no  connection  between  the  processes  of  adjacent  cells  except 
by  contact.  There  is,  therefore,  properly  no  nervous  network,  but  only  a 
dense  felt-work  of  interlacing  fibrils.  There  may  be  some  exceptions  ;  in 
recent  investigations  of  the  retina  and  of  the  electric  organ  of  the  torpedo 
nervous  networks  formed  by  the  processes  of  several  nerve-cells  have  been 
described.  In  general,  the  phrase  "  nervous  network  "  or  "  nervous  plexus  " 
is  to  be  interpreted  as  signifying  the  disposition  of  single  nerve-fibers  that 
branch  off  from  nerve-fiber  bundles  to  join  other  bundles.  The  transition  of 
one  nerve-fiber  into  another  never  occurs. 


Nerve-cell  of  th( 


Nerve-cell  of  the 
second  type. 


Fig.  39. — Two  Nb 
cylinder  or 


Nerve-Fibers. 

Dependent  upon  the  presence  or  absence  of  the  medullary  sheath,  nerve- 
fibers  are  divided  into  the  medullated  or  white  and  the  nonmedullated  or  gray. 
Each  division  is  susceptible  of  a  subdivision  dependent  on  the  presence  or 
absence  of  the  neurilemma. 

Nonmedullated  Fibers.  Without  a  Neurilemma. — These  consist  of 
the  naked  axis-cylinder  only,  and  are  found  in  the  olfactory  nerves,  where 
they  are  held  together  and  grouped  into  bundles  by  connective  tissue.  Similar 
are  many  fibers  of  the  sympathetic  nerve,  the  so-called   Remak's  fibers  ;   they 


8i 


are  transparent,  cylindrical,  or  band-like  in  form,  from  3  to  7  /i  wide,  about  2  ij. 
thick,  and  exhibit  faint  longitudinal  striation  ;  they  are  similarly  grouped 
into  bundles,  which  possess  an  imperfect  sheath  formed  by  closely  applied 
flattened  connective-tissue  cells  having  oblong  nuclei. 

While  the  fibers  described  above  exhibit  the  same  structure  throughout 
their  length,  there  are,  on  the  other  hand,  nerve-fibers  of  which  only  certain 
divisions  are  naked  axis-cylinders  ;  such  divisions  occur  as  the  peripheral  endings 
of  the  nerves  of  special  sense,  in  sensory  as  well  as  motor  nerves,  and  as  the 
proximal  portion,  coming  off  from  the  cell  as  the  axis-cylinder  process  (Fig. 
36,  a). 

Nonmedullated  Nerve-fibers.      With   a   Neurilemma. — These  con- 
sist of  the  axis-cylinder  enveloped  by  a  neurilemma,  and  are  of  the  same  struc- 
ture throughout  their  extent ;  they  are  found  in  many  invertebrates,  and  among 
vertebrates,    in   amphioxus,  and   in    cyclo- 
stoma.      They  occur  in  limited  portions  in 
the  course  of  the  cerebro-spinal  nerve-fibers 
(Fig.  36,  b). 

Medullated  Nerve  fibers. — Among 
these  is  none  which  possesses  the  medullary 
sheath  throughout  its  length ;  this  always 
invests  only  one  portion  of  the  fiber.  The 
medullated  fibers  may  be  icnthout  a  neuri- 
lemma, and  consist  of  the  axis-cylinder  and 
the  medullary  sheath  ;  such  fibers  occur  only 
in  the  central  nervous  system.  Medullated 
fibers  -with  a  neurilemma  are  found  in  the 
trunks  and  branches  of  the  cerebro-spinal 
nerves,  also  in  the  sympathetic  nerve,  and 
vary  in  thickness  from  i  to  20  ix.  The 
thickness  of  the  nerve-fiber  bears  no  rela- 
tion to  its  motor  or  sensory  nature,  but 
appears  to   be  determined    by  its   length : 

the  longer  its  course,  the  thicker  is  the  fiber.  Division  of  the  medullated 
fibers  occurs  (i)  throughout  the  central  nervous  system,  principally  where  the 
collateral  fibrils  diverge  at  right  angles  into  the  white  substance;  and  (2)  in 
the    peripheral   nervous    system    shortly    before    their    ultimate    distribution 

(Fig-  36)- 

The  medullated  nerve-fibers  have  a  brief  lease  of  life.  They  degenerate 
by  a  gradual  breaking  down  of  the  white  substance  and  the  axis-cylinder  into  a 
granular  mass  containing  numerous  nuclei;  in  this  mass  both  parts  are  regen- 
erated, the  axis-cylinder  probably  by  outgrowth  of  the  axis-cylinder  process  of 
the  nerve-cell. 

The  axis-cylinder,  the  essential  part  of  every  nerve-fiber,  occasionally 
exhibits  a  delicate  longitudinal  striation,  the  indication  of  its  fibrillar  structure. 
Each  fibrilla  represents  a  special  conducting  path  and  is  cemented  to  neighbor- 
6 


Sympathetic  Nerve  of  Rabbit,  i.  Non- 
medullated; 2, thin  medullated  nerve  fibers; 
3.  ganglion-cell;  characteristic  appearance 
of  the  nucleus  lost  after  treatment  with 
osmic  acid  ;  4,  nuclei  of  connective-tissue 
capsule :  5,  fine  conneclive-tissue  fibers. 
X  240.    Techn.  No.  32. 


82 


HISTOLOGY. 


ing  fibrilljE  by  a  small  amount  of  finely-granular  interstitial  substance — neuro- 
plasm. [A  delicate,  elastic,  special  investment  of  the  axis-cylinder — the  axi- 
lemma — is  described  by  Kiihne.      By  some  authors  it  is  regarded  as  an  artifact.] 

The  medullary  sheath  is  composed  of  a  semi-fluid,  highly  refracting,  fatty 
substance,  the  myelin,  which  imparts  to  fresh  medullated  fibers  the  appear- 
ance of  glistening  hyaline  cylinders,  homogeneous  throughout,  the  structure  ol 
which  can  only  be  perceived  by  the  help  of  reagents. 

In  favorable  conditions  it  may  be  seen  that  the  medullary  sheath  is  not 
continuous,  but  is  divided  at  slightly  irregular  intervals  by  oblique  incisions  or 
clefts  into  small  conical  or  funnel-shaped  pieces,  the  Schmidt- Lantennann  seg- 
ments (medullary  segments,  cylindro-conical  segments),  which  are  united  by 
cement-substance  (Fig.  41,  9).     Kolliker  has  latterly  interpreted  these  oblique 


6     7    8  9  10 


Fig.  41. — Medullated  Nerve-Fibers  from  the  Sciatic  Nerve  of  Frog.  X  280.  i.  Normal :  2,  shrunken  ; 
3,  tortuous  axis-cylinder;  4,  node  of  Ranvier;  5,  neurilemma  with  nucleus.  Techn.  No.  29.  6,  7,  8,  and 
9,  fresh  medullated  nerve-fibers  ;  10,  post-mortem  distortion  of  medullary  substance ;  r,  annular  constric- 
tion ;  /,  incisures  of  Lantermann  ;  ;",  medullary  segment.     Techn.  No.  27  a. 


markings  as  artifacts.  After  treatment  with  different  reagents,  the  apparently 
homogeneous  medullary  substance  of  fresh  nerve-fibers  in  dying  undergoes 
partial  transformation,  and  the  fibers  exhibit  a  characteristic  double  contour 
(thence  the  old  designation,  "double-bordered,"  or  "dark-edged"  fibers), 
and  later  appear  mottled,  owing  to  the  distortion  of  the  white  substance,  which 
collects  into  irregular  spherical  masses  (Fig.  41,  10).  [According  to  Kiihne 
and  Ewald  the  medullary  substance  consists  of  two  parts  :  a  reticulum  composed 
of  a  resistant  material  resembling  neurokeratin,  which  encloses  within  its  meshes 
the  other  part — the  myelin.  Owing  to  the  variability  in  the  appearance  of  the 
network,  other  authorities  regard  it  as  an  effect  of  the  reagents  employed  to 
demonstrate  it.] 

At  regular  intervals  along  the  medullated  nerve-fibers  the  medullary  sub- 


83 


stance  is  interrupted,  so  that  the  axis-cylinder  and  neurilemma  come  into  con- 
tact. At  these  points  the  fibers  exhibit  well-marked  annular  constrictions, 
termed  the  nodes  of  Ranvier  (Fig.  42).  These  constrictions  occur  in  all 
peripheral  medullated  fibers,  at  inter^'als  of  from  o.oS  mm.  in  thin,  to  i  mm. 
in  thick  fibers,  dividing  them  into  intcniodal  segments 
or  internodes.  In  the  vicinity  of  the  nodes  the  axis- 
cylinder  frequently  shows  a  biconical  enlargement, 
probably  due  to  a  local  accumulation  of  neuroplasm. 
After  treatment  with  silver  nitrate,  the  nodes  are 
rendered  conspicuous  by  a  dark  annular  disk  called 
the  constricting  band,  produced  by  the  staining  of 
the  cement-substance  collected  at  these  points,  and 
distinct  transverse  stride  (Frommann's  lines)  appear 
on  the  adjacent  parts  of  the  axis-cylinder.  [The 
stained  cement-substance  forms  the  transverse  bar, 
the  stained  axis-cylinder  the  vertical  bar  of  a  minute 
dark-brown  cross  ("silver  cross").  The  division 
of  a  medullated  nerve-fiber  always  occurs  at  the  site 
of  a  node  of  Ranvier.] 

The  neurilemma,  or  sheath  of  Schwann,  is  a 
delicate  structureless  membrane,  against  the  inner 
surface  of  which  lie  oval  nuclei  surrounded  by  a  very 
small  amount  of  protoplasm  (Fig.  41,  5). 

The  union  of  the  elements  of  the  nervous  tissues  in  the  peripheral  nerv- 
ous system  is  secured  by  means  of  connective  tissue,  which  contains  the  ramifi- 
cations of  the  blood-vessels.  In  the  central  nervous  system  they  are  supported 
and  held  together,  not  only  by  connective  tissue,  but  by  a  peculiar  form  of 
tissue,  the  neuroglia. 


J.  42. — Medullated  Nhrve- 

VITH    Su 


VER  Nitrate  Solu- 
560.  I.  At  r,  node  of 
Ranvier;  a,  axis-cylinder,  ol 
which  only  a  small  extent  is 
silvered  ;  I,  biconical  swellings 
displaced  downward  owing  to 
manipulation.  2  Axis-cylinder 
with  the  silvered  portion  in  situ, 
at  a.  3.  Axis-cylinder  with 
cross-markings.  Techn.  N0.31. 


II.  MICROSCOPIC  ANATOMY  OF   THE   ORGANS. 

I.  THE  CIRCULATORY  SYSTEM. 

THE  BLOOD-VESSELS. 
The  blood-vessels  are  composed  of  fibrous  connective  tissue,  elastic  fibers, 
and  smooth  muscle-fibers,  mingled  in  widely  different  proportions,  and  arranged 
in  strata  or  tunics.  In  general,  a  uniform  disposition  of  the  elements  prevails 
in  each  tunic  ;  longitudinal  in  the  inner  and  outer,  circular  in  the  middle  tunic. 
An  exception  to  this  occurs  in  the  complicated  structure  of  the  heart  and  in 
the  simple  structure  of  the  capillaries. 

The  Heart. 
The  walls  of  the  heart  consist  of  three  membranes  :    i,   the  endocardium  ; 
2,  the  powerfully  developed  muscular  layer;  3,  the  pericardium. 

The   endocardium    is  a   connective-tissue    membrane 
^  j,'^"^  which  contains  smooth  muscle-fibers  and  numerous  elastic 

1^  ^' „   ^"'        fibers.     The  latter  are  especially   well  developed  in    the 
'^Alr*"  ;:i>«        auricles,  where  they  form  a  close-meshed  network  or  are 
^  '-,C^>  blended  in  a  fenestrated  membrane  (Fig.  21).     The  free 

^.■^m— i.  surface,  that  directed  toward  the  cavity  of  the  heart,  is 

^   "  clothed  with  a  simple  layer  of  irregularly  polygonal  epithe- 

lial (endothelial)  cells. 

The  naked  miiscle-fihcrs,    whose   structure  has  been 

'"/""erimysfum      dcscribcd,  are  surrounded  by  a  delicate  perimysium,  and 

sw'ined il^ciei ;  r'.btood'-      are  United  by  numerous  lateral  processes.     The  arrange- 

No^al!  ^^-t"- '^  ='=''"•      ment  of  the  muscle-fibers  is  very  intricate.      The  muscle 

tissue  of  the  auricles  is  entirely  separate  from  that  of  the 

ventricles.     In  the  former  an  outer  transverse  layer,  common  to  both,  and  an 

independent  longitudinal  layer  in  each  can  be  distinguished.      In  addition, 

numerous  small  bundles  pursue  independent  courses  in  other  directions.     The 

muscle  tissue  of  the  ventricles  is  much  more  irregularly  distributed.    The  bundles 

extend    in   all  directions,   often   describing  a  figure-of-eight   in  their  course. 

Between  the  auricles  and  ventricles  lie  firm   tendinous  ligaments,  the  annuli 

fihrosi,  of  which  the  right  is  .stronger  than  the  left.     Similar  but  less  developed 

ligaments  lie  at  the  arterial  orifices  of  the  ventricles.     Numerous  muscle-fibers 

take  their  origin  in  these  ligaments. 

The  pericardium  is  a  connective-tissue  membrane  penetrated   by  elastic 
84 


Muscle-fiber; 


THE    CIRCULATORY    SYSTEM. 


85 


fibers,  clothed  on  its  outer  (visceral  layer)  and  inner  (parietal  layer)  surfaces 
by  a  single  stratum  of  epithelium.  The  parietal  pericardium  is  considerably 
thicker  than  the  visceral.      Between  the  latter  and  the  heart  fat-cells  are  found. 

The  valves  of  the  heart  are  composed  of  fibrous  connective  tissue,  contin- 
uous with  that  of  the  annuli  fibrosi,  and  their  surfaces  are  clothed  by  the  endo- 
cardium. Muscle-fibers  are  found  only  in  the  roots  or  attached  edges  of  the 
valves.  The  numerous  blood-vessels  of  the  muscular  wall  of  the  heart  form 
typical  capillary  networks  with  elongated  meshes  (see  the  Muscular  System). 
The  pericardium  and  endocardium,  the  latter  in  its  deeper  strata,  also  possess 
blood-vessels. 

The  lymph-vessels  are  extremely  numerous  in  the  heart.  They  form  a 
comprehensive  system  embracing  all  the  lymph-spaces  in  the  clefts  between  the 
muscle-fibers,  and  accompany  the  blood-vessels  in  their  course.  The  nerve 
supply  of  the  heart  includes  medullated  nerve-fibers  derived  from  the  pneumo- 
gastric  and  nonmedullated  sympathetic  nerve-fibers  from  the  cervical  ganglia ; 
along  their  course  numerous  ganglion-cells  occur. 


^?^^H 


Fig.  44.— Small  Aktbribs  of  Man.  i.  Nuclei  ot  intima,  the  outlines  of  the  cells  are  invisible;  m,  nucle 
of  circuLirly-disposed  musclc-fibers  of  media;  a,  nuclei  of  the  adventitia ;  A,  artery  with  the  surface  ir 
focus  ;  B,  artery  with  the  lumen  in  focus ;  at  m'  the  nuclei  of  the  muscle-fibers  of  the  media  are  seen  ii 
optical  section  ;  C,  small  artery  shortly  before  transformation  into  capillaries.  The  media  here  consists  of  a 
few  isolated  muscle-fibers.     X  240.     Techn,  No.  34  a. 


The  Arteries. 

The  walls  of  the  arteries  comprise  three  coats :  i,  tunica  intima  ;  2,  tunica 
media;  3,  tunica  adventitia.  The  elements  of  the  tunica  media  are  transversely 
disposed,  those  of  both  the  other  tunics  chiefly  longitudinally.  The  structure 
and  thickness  of  these  coats  varies  with  the  size  of  the  artery.  This  renders 
their  classification  as  small,  medium,  and  large  arteries  desirable. 

The  small  arteries  include  the  terminal  branches  shortly  before  their  trans- 
formation into  capillaries.  The  intima  consists  of  elongated,  spindle-shaped 
epithelial  cells  and  a  structureless  membrane,  the  so-called  internal  elastic  mem- 
brane, which  in  somewhat  larger  arteries  assumes  the  character  of  a  fenestrated 
membrane.  The  media  is  formed  of  a  single  layer  of  circularly-disjiosed 
smooth  muscle-fibers.     The  adventitia,  the  external  coat,  is  composed  of  Ion- 


86  HISTOLOGY. 

gitudinally-disposed  bundles  of  connective  tissue  and  fine  elastic  fibers.      It 
blends  insensibly  with  the  surrounding  connective  tissue. 

The  arteries  of  medium  size  comprise  all  the  arteries  of  the  body  with  the 
exception  of  the  aorta  and  the  pulmonary  artery.  The  intima  of  these  vessels 
has  increased  in  thickness  owing  to  the  interposition  between  the  endothelium 
and  internal  elastic  membrane  of  delicate  fibrous  connective  tissue,  flattened 
corpuscles,  and  networks  of  elastic  fibers.  This  subendothelial  layer  is  absent 
in  the  uterine  arteries  of  young  individuals,  in  the  coeliac,  external  iliac,  the 
renal,  and  the  mesenteric  arteries.  The  media,  in  addition  to  .several  super- 
imposed layers  of  circularly-arranged  smooth  muscle-fibers,  comprises  wide- 


FiG.  45.— Portion  of  Cross-Section  of  the  Brachial  Artehv  op  Man.     X  loo.    Techn.  No.  33. 

meshed  networks  of  elastic  fibers.  At  the  inner  boundary  of  the  media  of 
some  arteries  longitudinally-disposed  muscle-fibers  occur;  these  are  especially 
well-developed  in  the  subclavian  artery.  The  proportion  of  the  two  tissues  in 
the  different  arteries  is  extremely  variable.  In  the  coeliac,  femoral,  and  radial 
arteries  the  muscle  tissue  preponderates ;  in  the  carotid,  axillary,  and  common 
iliac,  the  elastic  tissue.  The  adventitia  has  also  become  stouter.  Thick  elastic 
fibers  occur  in  especial  profusion  at  the  boundary  of  the  media  and  in  many 
arteries  form  a  continuous  layer  designated  the  external  elastic  membrane. 
New  elements  in   the  adventitia  of  medium  size  arteries  are  smooth  muscle- 


THE   CIRCULATORY    SYSTEM. 


87 


fibers,  which  appear  in  single  longitudinally-disposed  bundles,  and  never  form  a 
continuous  layer. 

In  the  large  arteries  (aorta  and  pulmonary  artery)  the  epithelial  cells  of 
the  intima  are  broader  and  more  polyhedral  in  outline  than  in  medium-sized 
vessels.  The  subepithelial  layer  consists  of  fibrous  connective  tissue,  elastic 
networks,  and  flattened,  stellate,  or  spherical  cells.  The  elastic  network  is 
closer  meshed  the  nearer  to  the  intima  it  is,  and  finally  passes  into  a  fenestrated 
membrane  corresponding  to  the  internal  elastic  membrane  of  small  and  medium- 


FlG.  46. — ENUnxHBLIUH    OF  A  MkS-  Fig.    47. — Pll 

BNTBKic  Aktrryop  Raubit.    Sur- 
face vicw.     X260.     Tcchn,  No.  35. 


■  Cross-Sbction  op  Thoracic  Aokta  op  Ma 
X  100.    Techn.  No.  33. 


sized  arteries.  The  media  of  the  large  arteries  is  characterized  by  the  prepon- 
derance of  elastic  tissue  over  the  muscular  elements.  The  thin  elastic  networks 
of  the  media  of  medium-sized  arteries  is  here  replaced  by  close  networks  of 
broad  elastic  fibers  or  by  fenestrated  membranes,  which  alternate  regularly  with 
the  lamellne  of  smooth  muscle-fibers.  The  elastic  elements,  like  the  muscle- 
fibers,  are  circularly  arranged.  The  muscular  lamellae  are  penetrated  in  an 
oblique  direction  by  elastic  fibers  which  connect  all  the  elastic  elements  of  the 
media.     The  media  of  the  larger  medium-sized  arteries  possess  the  elastic 


»S  HISTOLOGY. 

membrane;  it  is  well-marked  in  the  carotids,  which  closely  approach  in  struct- 
ure the  large  arteries.  The  adventitia  of  large  arteries  presents  no  essential 
peculiarity  and  differs  but  slightly  from  that  of  the  medium-sized  arteries.  It 
does  not  possess  the  external  elastic  membrane.  In  the  lower  animals  smooth 
muscle-fibers  are  present. 

The  Veins. 
There  is  no  definite  proportion  between  the  size  of  the  veins  and  the 
thickness  of  their  walls,  and  no  basis  for  a  division  into  groups  as  with  the 
arteries.  The  veins  are  characterized  by  the  preponderance  of  fibrous  connec- 
tive tissue,  and  the  slighter  development  of  the  muscular  and  elastic  elements. 
Three  coats,  as  in  the  arteries,  may  be  distinguished.  Owing  to  the  meager 
development  of  the  media  some  histologists  have  suggested  that  only  two  coats 
are  present,  the  tunica  intima  and  tunica  adventitia,  and  that  the  layers  usually 
regarded  as  tunica  media  belong  to  the  latter.      The  intima  consists  of  a  single 


Smooth  muscle-fibers  of  the  adventitia. 
Cross-Section  through  a  Vein  op  Lime  of  Man.     X  loo.    Techn.  No.  33. 


layer  of  endothelial  cells  which  are  elongated  only  in  the  smallest  veins,  in 
others  are  polygonal  in  outline.  In  medium-sized  veins,  2  to  9  mm.  in  diame- 
ter, nucleated  connective-tissue  elements  occur  in  the  subendothelial  layer, 
which  in  large  veins  (femoral,  popliteal,  and  superior  cava)  is  arranged  in 
distinct  lamellag.  Surrounding  this  is  the  internal  elastic  membrane,  which  is 
structureless  in  small  veins,  but  in  medium-sized  and  large  veins  it  is  represented 
by  elastic  networks.  Oblique  and  longitudinally-disposed  smooth  muscle- 
fibers  occur  in  the  intima  of  the  iliac,  femoral,  saphenous,  and  mesenteric 
veins. 

The  media  exhibits  great  variation.  It  is  composed  of  circular  muscle- 
fibers,  elastic  networks,  and  fibrous  connective  tissue,  and  is  best  developed  in 
the  veins  of  the  lower  extremities  (especially  in  the  popliteal),  less  in  the  veins 
of  the  upper  extremities,  still  less  in  the  large  veins  of  the  abdominal  cavity, 
and  is  absent  in  many  veins  (those  of  the  pia  and  dura,  the  bones,  and  the 


THE    CIRCULATORY    SYSTEM.  89 

retina,  in  the  superior  cava,  and  also  in  the  veins  proceeding  from  the  capil- 
laries). 

The  usually  well-developed  adventitia  consists  of  intercrossing  bundles  of 
connective  tissue,  elastic  fibers,  and  longitudinally-disposed  smooth  muscle- 
fibers,  which  are  more  highly  develo])ed  in  the  veins  than  in  the  arteries. 
The  adventitia  of  certain  veins  (the  trunk  of  the  portal  and  the  renal)  possesses 
an  almost  complete  membrane  of  longitudinally-arranged  muscle-fibers  (Fig. 

49)- 

The  valves  of  the  veins  are  folds  of  the  intima,  covered  on  both  surfaces 
by  epithelial  cells,  which,  on  the  surface  directed  toward  the  vascular  stream, 
are  elongated  in  the  direction  of  the  current  ;  on  the  opposite  surface,  toward 
the  wall  of  the  veins,  they  are  elongated  transversely. 


The  Capillaries. 

The  capillaries  establish  the  communication  between  the  arteries  and 
veins.  There  are  a  few  exceptions,  as  for  example  in  the  corpora  cavernosa. 
In  the  transformation  of  the  arteries  into  capillaries  a  gradual  simplification 
of  the  structure  of  the  vessel-wall  follows 

(Fig.   44).     The  media  grows  continu-  imima.  ^ — —-^—-^----^^^^ 

ally  thinner,  until  in  the  vessels  between  '      "  '  'Cy's?^ /~^i,t^   _^ 

the  smallest  arteries  and  capillaries  it  is  Adventiiiawithcro«.j  ',  '^'^^«^a  . 
represented  by  a  few  isolated  circular  n"  fiTe's. °"^' "  '  j  ■^^-^■^^'^M 
muscle-fibers,  at.wide  intervals,  that  ulti-  ~     -~^-^- 

mately  disappear  entirely.  The  advcn-  ■■' o;*Ji7J:"°^o.^">e'hi°NlT3- '*'"''*'' ^"^ 
titia  becomes  correspondingly  attenu- 
ated until  it  consists  of  a  thin  layer  of  connective-tissue  fibers  and  corpuscles 
that  also  ultimately  vanish,  so  that  at  the  last  the  only  part  of  the  vessel-wall 
that  remains  is  the  intima.  This  is  also  reduced  to  a  stratum  of  plate-like, 
nucleated  endothelial  cells.  The  walls  of  the  capillaries,  therefore,  consist  of 
a  simple  layer  of  endothelial  cells,  spindle-shaped,  and  united  at  their  edges 
by  a  small  amount  of  cement-substance. 

The  capillaries  divide  without  decrease  in  caliber  and  by  anastomosis  with 
neighboring  capillaries  form  networks  differing  widely  in  the  size  of  their 
meshes.  The  closest  meshes  occur  in  the  capillary  networks  of  secretory 
organs,  as  in  the  lung  and  the  liver  ;  wide-meshed  networks  in  the  muscles, 
the  serous  membranes,  and  the  special  sense  organs.  The  reverse  obtains 
with  regard  to  the  caliber  of  the  capillaries ;  the  widest  capillaries  are  found 
in  the  liver,  the  narrowest  in  the  retina  and  in  the  muscles. 

Development  of  Capillaries. — Only  the  developmental  processes  in  the  post- 
embryonic  epoch  will  be  considered  here.  A  minute  conical  mass  appears  on 
the  wall  of  an  existing  capillary,  resting  with  a  broad  base  on  the  latter  and 
having  a  tapering,  sharp-pointed  free  end.  In  the  further  course  of  develop- 
ment this  pointed  free  end  unites  with  another  off-shoot  arising  from  a  different 
point  on  the  capillary  wall.     They  are  solid  at  first  but  gradually  become  hoi- 


90  HISTOLOGY. 

low  by  an  extension  of  the  lumen  of  the  capillary,  and  subsequently  the  walls 
of  the  new  vessels  become  differentiated  to  endothelial  cells.  The  development 
of  new  capillaries  is  always  consummated  in  connection  with  existing  capillaries. 
These  blind  capillary  sprouts  may  be  hollowed  out  at  an  early  period  ;  corpus- 
cles that  flow  into  them  disintegrate  because  they  are  excluded  from  the  circu- 
lation and  the  interchange  of  gases.  They  fall  into  fragments,  which  have 
been  erroneously  interpreted  as  hematoblasts ;  they  have  no  connection  with 
the  true  hematoblasts. 

All  medium  and  large  blood-vessels  possess  small  blood-vessels  (vasa 
vasorum)  that  provide  for  the  nutrition  of  their  walls  ;  they  run  almost 
exclusively  in  the  adventitia.     The  intima  is  always  without  blood-vessels. 

All  blood-vessels  are  furnished  with  nerves,  which  form  a  plexus  of  medul- 
lated  fibers  in  the  media  of  the  arteries  and  veins.  From  these,  nonmedullated 
fibers  arise  which  are  distributed  to  the  muscle-fibers.      The  capillaries  are 


55=0.0     C)°''g      O 


Fig.  50. — Surface  View  of  a  Portion  of  the  Greater  Omentum  of  a  Seven-Days*  Rabbit,  c. 
Blood  capill.*ries,  some  containing  blood-corpusclcs  ;  j,  capillary  sprout  tapering  to  a  free  solid  point;  :', 
voung  capillary,  the  greater  part  of  which  is  hollow  ;  at  s'  still  solid  ;  k,  nuclei  of  peritoneal  endothelium. 
X  240.    Techn.  No.  37. 

accompanied  by  encircling  networks  of  delicate  nonmedullated  nerve-fibers. 
Many  blood-vessels  are  surrounded  by  lymph  channels  ;  occasionally  the  lymph- 
spaces  in  the  adventitia  unite  to  form  a  complete  ensheathing  sinus,  the  adven- 
titial or  perivascular  lymph-space. 


The  carotid  gland  is  really  no  gland  but  consists  essentially  of  blood- 
vessels. The  capillaries  arising  from  the  division  of  the  single  arterial  vessel 
differ  greatly  in  width,  and  are  surrounded  by  numerous  cells  resembling  the 
plasma-cells  of  connective  tissue,  arranged  in  rounded  groups  forming  the  so- 
called  secondary  nodules.  The  veins  are  collected  at  the  periphery  of  the 
organ,  which  besides  contains  fibrous  connective  tissue,  isolated  ganglion-cells, 
and  a  conspicuous  number  of  medullated  and  nonmedullated  nerve-fibers. 
Similar  in  structure  is  the  coccygeal  gland,  the  blood-vessels  of  which  are  char- 
acterized by  hemispherical  evaginations. 


the  circulatory  system.  9i 

The  Blood. 

The  blood  is  a  slightly  clammy,  red-colored  liquid  which  consists  of  a 
fluid  substance,  the  blood-plasma,  and  formed  elements,  the  blood-cells,  the 
blood-platelets,  and  elementary  granules.  The  blood-cells  are  of  two  kinds  : 
colored  blood-cells  and  colorless  blood-cells. 

The  colored  blood-cells  are  soft,  flexible,  highly-elastic  elements,  and  pos- 
sess smooth,  slippery  surfaces.  In  man  and  in  other  mammals  they  have  the 
form  of  a  flat-circular  disk,  slightly  concave  on  each  surface,  and  therefore  re- 
semble biconcave  lenses.  (Exceptions  occur  in  the  llama  and  the  camel,  in 
which  the  colored  blood-cells  are  oval. )  The  average  diameter  in  man  is  7.  s  /t, 
the  thickness  1.5  11.  The  colored  blood-corpuscles  of  domesticated  mammals 
are  all  smaller,  the  largest  are  those  of  the  dog  (7.3  //)•  The  colored  blood- 
cells  consist  of  a  stroma  (protoplasm),  the  spaces  of  which  are  filled  with  the 
blood-coloring  matter,  the  hemoglobin.  The  hemoglobin  imparts  to  the  cor- 
puscle its  yellow  or  yellowish-green  color.     A  nucleus  and  a  proper  cell-mem- 


FlG.  51. — Blood. Corpuscles  Magnified  560  Times.  /I.  Of  man:  1-6.  Discoidal  cotored  blood-ccIU;  i,  seen 
with  close  focus;  2,  with  distant  focus;  3  and  4,  viewed  edgewise;  5,  crenaled  In  consequence  of  evapo- 
ration ;  6.  after  treatment  with  water ;  7,  spherical  colored  blood^corpuscle  ;  8.  colorless  blood-corpuscle  ; 
9,  blood-platelets.  />.  Of  frog:  10-13.  Colored  blood-cells;  10,  fresh  nucleus,  indistinct;  11,  a  few 
minutes  later,  nucleus  plainly  visible  ;  12,  seen  from  the  side ;  13,  after  treatment  with  water;  14,  living  ; 
15,  dead  colorless  blood-corpuscle.    Techn.  Nos.  38-41. 

brane  are  wanting.  The  colored  blood-corpuscles  ol  fishes,  amphibians,  rep- 
tiles, and  birds  are  distinguished  from  those  of  mammals  by  their  oval,  bicon- 
vex form,  their  generally  greater  size  (22  ,«  long  by  15  /m  broad  in  the  frog),  as 
well  as  by  the  presence  of  a  round  or  oval  nucleus ;  in  other  respects  they 
exhibit  the  same  properties  as  those  of  mammals. 

The  white  or  colorless  blood-cells  (leucocytes)  occur  not  only  in  the  blood 
but  also  in  the  lymphatic  vessels,  where  they  are  termed  lymph-corpuscles. 
They  are  also  found  outside  of  the  vessels,  in  bone-marrow,  in  adenoid  tissue, 
in  fibrous  connective  tis.sue,  and  also  between  epithelial  and  gland-cells,  where 
they  have  wandered  by  their  power  of  amoeboid  movement,  and  are  therefore 
described  as  "  wandering  cells." 

The  colorless  blood-cells  consist  of  a  clammy  protoplasm  and  a  nucleus, 
and  are  without  a  cell-membrane.  A  definite  form  cannot  be  described, 
because  during  life  they  are  engaged  in  amoeboid  activity.  In  a  condition  of 
rest  they  are  spherical  (Fig.  52). 


92  HISTOLOGY. 

Their  size  and  the  properties  of  the  nucleus  and  protoplasm  have  led  to 
the  following  classification  : 

1.  The  smallest  leucocytes,  measuring  4  to  7.5  /i.  They  possess  a  propor- 
tionately large  round  nucleus  surrounded  by  a  narrow  zone  of  protoplasm,  so 
small  in  amount  that  it  can  scarcely  be  demonstrated  by  the  usual  methods 
(Fig.  52,  a).  These  are  regarded  as  young  forms;  they  exhibit  little  activity 
and  are  found  chiefly  in  adenoid  tissue. 

2.  The  second  kind  have  a  diameter  of  7.8  to  10  p. ;  their  nucleus  is  spheri- 
cal and  surrounded  by  a  larger  amount  of  granular  protoplasm.  The  nucleus 
may  be  cleft  or  lobulated  (Fig.  52,  i).  Occasionally  several  disjoined 
nuclei  are  present ;  the  slender  filaments  uniting  the  several  parts  of  the 
lobulated  nucleus  are  frequently  overlooked,  which  then  simulates  several 
separate  nuclei.  The  latter  form  is  very  active  ;  the  lobulation  of  the  nucleus 
is  in  fact  the  expression  of  this  activity ;  seventy-seven  per  cent,  of  the  leuco- 
cytes of  the  blood  are  of  this  form. 

3.  The  third  kind  of  leucocytes  measure  from  8  to  14  p.,  and  are  charac- 
terized by  their  granular  protoplasm  ;  the  granules  are  variable  in  quantity  and 

react  differently  to  stains.     According  to  their  affinity  for 

@acid,    basic,    or   neutral    dyes,   oxyphile,    basophile,   and 
(*^  neutrophile  leucocytes  are  distinguished.* 

"^       '  -C"^^*^  '"'^'^  determination  of  the  proportionate  number  of,  as 

'©'  ^5^    ^2^  well   as    the    ratio    between,    the    colored    and    colorless 

Fig.  52.— Colorless      blood-corpuscles  is  coupled  with   considerable  difficultv, 

Blood-CellsofMan.  y  t-  ]■: 

c.  Cell  with  neutrophile      and  oulv  approximately-correct  estimates  can  be  siven. 

granules.  X  600.  Tcchn.  ,. 

No.  39.  In    man   one   cubic  millimeter  of  blood   contains   about 

5,000,000  colored  corpuscles.  The  white  blood-cor- 
puscles are  present  in  the  blood  in  much  smaller  number,  about  i  to  300  to 
500  colored. 

The  blood-platelets  are  very  unstable,  colorless,  round  or  oval  disks  having 
a  diameter  one-third  to  one-fourth  less  than  that  of  the  colored  blood-cells  ;  at 
times  they  are  present  in  the  blood  in  large  numbers.  A  leading  role  in  the 
process  of  coagulation  of  the  blood  is  ascribed  to  them. 

The  elementary  granules  are  for  the  most  part  fatty  granules  transferred 
from  the  chyle  to  the  blood.  They  are  frequently  observed  in  the  blood  of  the 
lower  mammals,  but  are  not  normally  present  in  the  blood  of  man. 

After  death,  or  as  a  result  of  changes  within  the  vessel-walls,  the  blood, 
under  the  influence  of  two  substances  which  pass  into  solution  in  the  plasma, 
fibrinoplastin  and  fibrinogen,  coagulates,  and  fibrin  is  formed.  The  coagulated 
blood  separates  into  two  parts,  the  clot  and  the  serum.  The  clot  is  red,  and 
contains  all  the  colored  and  the  majority  of  the  colorless  blood -corpuscles  and 
the  fibrin,   which    microscopically   consists  of   a  feltwork  of  fine,  straight, 


*Ehrlich,  who  made  this  classification,  proceeds  therein  from  a  different  standpoint  than 
that  of  the  chemist ;  acid  colors  are  those,  for  example,  with  which  acids  develop  the  coloring 
principle. 


THE    LYMPHATIC    SYSTEM.  93 

interlacing  filaments.  Chemically  fibrin  resembles  glutinous  connective  tissue. 
The  supernatant  serum  is  colorless  and  contains  a  few  colorless  blood-cells. 

The  coloring  substance  contained  in  the  colored  corpuscles,  x!nt  hemoglobin, 
crystallizes  under  certain  conditions,  and  in  nearly  all  vertebrates  the  crystals 
belong  to  the  rhombic  system.  Their  form  in  the  different  animals  varies 
greatly  ;  in  man  it  is  usually  prismatic.  Hemoglobin  is  readily  decomposed. 
One  of  the  decomposition  products  is  hematin,  which  yields  hematoidin  and 
hemin.  Crystals  of  hematoidin  occur  within  the  body  in  old  extravasated 
blood,  for  example,  in  the  corpus  luteum,  and  are  rhombic  prisms  of  orange- 
red  color.  The  hemin  crystals,  when  well-developed,  are  rhombic  plates  or 
needles  of  a  mahogany-brown  color.  They  are  often  very  irregular  in  form, 
and  as  a  positive  indication  of  the  presence  of  blood  have  an  important  legal 
relation. 

Development  of  Colored  Corpuscles. — From  the  earliest  period  of  embryonic 
development  and  during  the  whole  of  life  nucleated  colored  blood-cells  (hema- 
toblasts,  erythroblasts)  are  found  in  certain  situations.  Their  number  fluctu- 
ates and  runs  parallel  to  the  energy  of  the  blood-forming  processes.      By  indi- 


FlG.  53. — I.  Hemin  crystals  of  man;    whetstone  forms  on  the  right.    3.  Crystals  ol  ( 

toidin  crystals  of  man,  magnified  560   times.     4.  Hemoglobin  crystals  of  the  dog,  magnified   ico  times; 
*T,  a  crystal  showing  a  tendency  to  fall  apart  lengthwise.     Techn.  No.  44. 

rect  division  they  give  rise  to  the  nonnucleated  colored  blood -corpuscles, 
which  at  first  contain  a  nucleus,  but  lose  it  later.  As  centers  for  the  formation 
of  blood  in  the  embryo  the  liver  and,  later,  the  spleen,  in  the  adult  exclusively 
the  bone-marrow,  may  be  mentioned. 


2.    THE  LYMPHATIC  SYSTEM. 

THE  LVMPH-VESSELS. 

The  walls  of  the  larger  lymph-vessels,  from  0.8  to  0.2  mm.,  like  the 
blood-vessels,  are  composed  of  three  coats.  The  intima  consists  of  endothelial 
cells  and  a  network  of  delicate  elastic  fibers  with  elongated  meshes.  The  media 
is  formed  of  circularly-disposed  smooth  muscle-fibers  and  a  few  elastic  fibers. 
The  walls  of  the  smallest  lymph-vessels  and  the  lymph-capillaries  are  composed 
exclusively  of  extremely  delicate  endothelial  cells,  often  having  sinuous  outlines. 
The  lymph-capillaries,  unlike  the  blood-vessels,  present  at  frequent  intervals 
constrictions  and  dilatations,  and  where  they  branch  are  often  considerably 
widened  ;  the  networks  they  form  are  more  irregular. 


94 


HISTOLOGY. 


The  question  as  to  the  origin  of  the  lymph-vessels  is  not  yet  satisfactorily 
determined ;  while  some  authors  are  of  the  opinion  that  the  lymph-capillaries 
form  a  closed  system,  according  to  another  view,  widely  entertained,  the 
lymph-capillaries  are  open  toward  the  periphery,  and  are  in  direct  con- 
nection with  the  system  of  intercommunicating  cell-spaces  of  connective  tissue. 
These  interfascicular  clefts  are  by  some  set  apart  as  "  lymph  canaliculi  "  from 
the  lymph-vessels  with  well-defined  walls  composed  of  continuous  layers  of 
cells  ;  other  authors  include  the  lymph-canaliculi  in  the  lymph-vessels. 

According  to  the  first  opinion  the  surplus  of  nutritive  fluids  (tissue-juices) 
diffused  through  the  walls  of  the  blood -capillaries,  and  not  used  in  the  nutrition 
of  the  tissues,  is  returned  to  the   closed  lymph-capillaries  by  endosmosis  ;  the 
second  view  holds  that  the  tissue-juices  pass  directly 
from  the  tissue  into  the  patent  orifices  of  the  lymph- 
capillaries. 

It  is  a  significant  fact  that  the  lymph-vessels  of 
the  pleura  and  of  the  peritoneum  are  in  open  com- 
munication with  their  respective  cavities  through 
small  openings — stomata — between  the  endothelial 
cells,  which  in  the  pleura  are  found  at  the  intercostal 
1^^  spaces,  and  in  the  peritoneum  on  the  central  tendon 
of  the  diaphragm. 


BIT,  showing  the  boundaries  of 
the  endothelial  cells.  X  50. 
Techn.  No.  35. 


The  Lymph-Nodes. 
The  lymph-nodes  (incorrectly  "lymph-glands") 
are  macroscopic,  encapsuled  bodies  found  along  the 
course  of  the  lymph-vessels ;  they  are  usually  rounded, 
oval,  or  flat,  kidney-shaped  structures,  and  differ 
greatly  in  size.  At  one  side  there  is  often  a  scar- 
like depression,  the  hikes,  at  which  the  efferent 
lymph-vessels  emerge.  The  afferent  lymph-vessels 
penetrate  the  nodes  at  various  points.  Their  con- 
struction becomes  intelligible  if  we  proceed  from  the  following  conception  :  in 
certain  localities  three  to  six  lymph-vessels  divide  and  anastomose,  forming  a 
kind  of  rete  mirabile,  and  then  reunite  into  the  same  or  a  less  number  of 
usually  narrower  lymph-vessels.*  The  dividing  lymph-vessels  are  called  afferent 
(vasa  afferentia),  the  reunited,  efferent  vessels  (vasa  efferentia).  Within  the 
meshes  of  this  reticulum  lie  spherical  and  elongated  masses  that  consist  of 
adenoid  tissue.  The  spherical  masses,  the  scco?idary  nodules  (follicles),  occupy 
the  periphery ;  the  elongated  masses,  the  medullary  cords,  the  center  of  the 
lymph-node. 


*  Retia  mirabilia  were  first  described  in  connection  with  the  blood-vessels.  They  occur 
along  the  course  of  both  arteries  and  veins  ;  the  vessel  suddenly  breaks  up  into  branches  and 
these  into  capillaries,  which  reunite  into  a  single  vessel.  Exquisite  examples  of  such  networks 
occur  as  the  glomeruli  of  the  kidneys. 


THE    LYMPHATIC    SYSTEM. 


95 


The  node  is  enveloped  in  a  capsule  of  fibrous  connective  tissue,  which 
sends  into  the  interior  of  the  organ  stout  fibrous  bundles,  the  trabeciilce  (Fig. 
55).  Finer  extensions  from  the  trabecule  form  a  reticulum  which  breaks 
through  the  walls  of  the  lymph-vessels,  penetrates  the  secondary  nodules  and 
the  medullary  cords,  and  forms  a  support  for  the  numerous  leucocytes  present. 

The  lymph-nodes  consist  of  a  cortical  and  a  medullary  region  that  vary 
greatly  in  their  proportionate  extent.  The  cortex  contains  the  secondary 
nodules,  which  are  directed  toward  the  center  of  the  organ  and  merge  into  the 
medullary  cords  (Fig.  55).  The  secondary  nodules  and  medullary  cords  are 
surrounded  by  the  sinus-like  continuations  of  the  afferent  lymph-vessels.  The 
latter,  in  this  situation,  are  greatly  expanded  and  are  termed  lymph-sinuses ;  they 
are  interwoven  with  the  connective-tissue  reticulum.  The  lymph-vessels  never 
penetrate  the  interior  of  the  secondary  nodules.  The  secondary  nodules  and 
the  medullary  cords  are  composed  of  adenoid  tissue ;  that  is,  of  a  reticulum  of 
connective  tissue  the  meshes  of  which  are  crowded  with  leucocytes.  In  many 
of  the  secondary  nodules  there  is  a  light,  rounded  area,  xht  germinal  center,  in 


Medullary  cords.    "  Follicle."     Lyniph-s 


Fig.  55. — Section  op  a  Lymphatic  Nodulb  op 


'  Cat.     X  30.    Techn.  No.  47. 


which  karyokinetic  figures  are  always  to  be  found.  Multiplication  of  cells  also 
occurs  in  the  medullary  cords,  but  in  a  much  slighter  degree.  The  secondary 
nodules  are,  therefore,  centers  for  the  formation  of  the  leucocytes,  which  pass 
into  the  lymph-sinuses  and  thence  into  the  vasa  efferentia. 

The  ca])sule  consists  of  fibrous  connective  tissue  and  smooth  muscle-fibers, 
which  in  the  large  lymph-nodes  of  some  animals  are  arranged  in  bundles.  The 
trabeculae  have  the  same  structure ;  they  pass  between  the  secondary  nodes  and 
medullary  cords  but  do  not  come  into  contact  with  them,  being  separated  from 
them  by  the  lymph-sinuses.  The  walls  of  the  lymph-sinuses  are  formed  of  a 
simple  layer  of  plate-like  cells  ;  similar  cells  clothe  the  surface  of  the  nodules 
and  the  cords,  and  are  applied  to  the  trabeculae  and  the  connective-tissue 
reticulum. 

The  structure  of  the  lymph-nodes  is  difficult  to  recognize,  owing  to  several 
complications.  These  consist  in:  i,  the  merging  of  neighboring  secondary 
nodules ;  2,  the  anastomosis  of  the  medullary  cords  in  the  form  of  a  coarse 
network ;    3,  the  network  formed  by  the   trabeculx  ;    4,    the  interlacing  of 


96  HISTOLOGY. 

the  networks  formed  by  the  medullary  cords  and  the  trabecular ;  5,  the  pres- 
ence of  leucocytes  in  the  lymph-sinuses,  which  must  be  removed  by  special 
methods.  The  secondary  nodules,  the  medullary  cords,  and  the  leucocytes  in 
the  lymph-sinuses  form  a  soft  mass,  \ht  pulp  or  parenchyma  of  the  lymph-node. 
The  majority  of  the  blood-vessels  enter  at  the  hilus,  the  others  at  various 
points  on  the  surface  of  the  node.  The  latter  are  smaller  vessels  and  divide  in 
the  capsule  and  in  the  large  trabecule,  in  the  axes  of  which  they  run.  The 
large  artery  entering  at  the  hilus  divides  into  a  number  of  branches,  which  are 
surrounded  by  a  richly-developed  connective  tissue.  The  branches  are  prin- 
cipally distributed  to  the  adenoid  tissue,  only  a  few  entering  the  trabeculae  ; 
they  pass  through  the  lymph-sinuses,  to  the  medulla  and  to  the  cortex, 
and  in  both  situations  break  up  into  rich  capillary  networks,  which  supply  the 
oxygen  needed  in  the  formation  of  leucocytes.     The  veins  emerge  at  the  hilus. 


— ^  Medull.-^ry  cords. 


Fig.  56— From  a  Section  through  the  Medulla  of  a  Lymphatic  Nodule  of  Ox.  X  5°-  '"  '•":  upper 
half  the  trabeculae  and  medullary  cords  are  cut  lengthwise,  in  the  lower  half  crosswise.  Both  form  an  anas- 
tomosing network.  In  the  lymph-sinuses  fine  fibers  of  reticular  connective  tissue  are  seen,  which  still  in  part 
contain  leucocytes.     Drawn  with  change  of  focus,     'lechn.  No.  48. 

The  nerves  are  few  in  number,  the  supply  including  bundles  containing 
both  meduUated  and  nonmedullated  fibers  ;  their  ultimate  distribution  is  still 
undetermined. 

The  Peripheral  Lymph-Nodules. 
Adenoid  tissue  is  not  confined  to  the  lymph-nodes,  but,  in  different  degrees 
of  development,  occurs  widely  distributed  in  many  mucous  membranes ; 
sometimes  as  diffuse,  sometimes  as  definitely-circumscribed  infiltrations  of  leuco- 
cytes. These  formations  are  not  included  in  the  lymphatic  system.  More 
highly-specialized  structures,  nodules  with  germinal  centers,  resembling  exactly 
the  secondary  nodules  of  the  lymph-nodes,  are  also  found  in  the  mucous  mem- 
branes ;  these  are  termed  the  peripheral  lymph-nodes,  and  included  in  the  lymph- 
atic system.  In  many  mucous  membranes  they  occur  isolated,  as  the  solitary 
nodules  (solitary  follicles),  or  grouped,  as  "  Peyer's  patches,"  and  lie  always 
in  a  simple  layer  in  the  membrana   propria  close  to    the  epithelium    (see   the 


THE    LYMPHATIC    SYSTEM. 


97 


DigestiYC  Organs).  The  number  and  distribution  of  the  peripheral  lymph- 
nodes  is  subject  to  considerable  fluctuation,  not  only  in  the  different  species  of 
animals,  but  in  different  individuals  ;  since  their  mass  varies  and  there  are  fre- 
cjuent  transitions  from  circumscribed  to  diffuse  infiltration,  it  is  probable  that 
they  are  temporary  structures,  that  arise  and  disappear  during  life.  The 
follicles  are  distinguished  from  the  real  lymph-nodes  by  the  absence  of  the 
encircling  lymph-sinus.  The  only  exceptions  occur  in  the  rabbit,  in  which 
the  sinus  is  present  in  the  Peyer's  patches,  but  not  in  the  solitary  follicles. 
But  the  possession  of  a  germinal  center,  a  brooding-place  for  young  leucocytes, 
appears  in  so  far  to  entitle  them  to  a  place  in  the  lymphatic  system.  The 
young  leucocytes  only  in  part  enter  the 
Ivmijh-vessels  :     many    wander    through  ,.      , 

the    epithelium    to    the    surface    of    the 
mucous  membrane. 


Tin;  Lymph. 
The    lymph   is  a  colorless   fluid    in 
which  leucocytes  ( lymph-corpuscles)  and 
granules  are  suspertded.     The  latter  are 
immeasurably  small,  consist  of  fat,  and  M.iipighi.in  -:  ' 

are  found  principally  in  the  lymph-  (or         corpusccs. 
chyle-)  vessels  (lacteals)  of  the  intestine  ; 
frequently  they  are  present  in  enormous  ''"'p-' 

numbers  ;  they  impart  the  white  color  to  '  fl 

the   chyle.      In   other  Ivmph-vessels    the         „ 


ii 


fatty  granules  occur  but  sparingly.  -.-Il 

The  Spleen.  '  . ''' 

The    spleen    is    a    "blood-vessel 
gland  ■  •  consisting  of  a  connective-tissue      ^'t.^i^^Z.^Js^^^t^^.^^^^^cZ 
capsule  and  of  a  soft  red  mass,  the  spleen        ^'fTe'Hgiu  ta'^;ch"o'fTh""V«?y*'har"cS 
pulp,  which  is  composed  of  blood-vessels        no!V='^"'''  "^ "''""'''  "''"■   ^  '°'    ' "''"' 
and  adenoid  tissue. 

The  capsule  is  invested  by  a  reflection  of  the  ]jeritoneum,  with  which  it  is 
firmly  united.  It  is  composed  of  dense  fibrous  connective  tissue  and  a  net- 
work of  elastic  fibers.  In  some  animals  (the  dog,  cat,  pig,  etc.),  but  not  in 
man,  smooth  muscle-fibers  are  also  present.  Numerous  cylindrical  or  band-like 
prolongations,  the  irabecuhe,  extend  into  the  interior  of  the  organ,  where  they 
form  a  framework  in  the  spaces  of  which  lies  the  spleen  pulp.  In  the  lower 
mammals  the  trabeculte  also  contain  smooth  muscle-fibers.  At  the  hilum  of 
the  spleen  the  capsule  furnishes  special  sheaths  for  the  blood-vessels — adven- 
titial sheaths — which  blend  with  the  adventitia  of  the  latter  and  accompany 
them  for  long  distances.  The  sheaths  of  the  arteries  are  the  seat  of  numerous 
leucocytes,  which  form  a  continuous  envelope  along  the  entire  course  of  the 
7 


HISTOLOGY. 


vessel,  as  in  the  guinea-pig,  or,  as  in  man,  the  cat,  etc.,  are  limited  to  certain 
points  where  they  form  spherical  masses,  0.2  to  9.7  mm.  in  size,  the  so-called 
Malpighian  corpuscles.  Between  these  many  intermediate  forms  exist,  as  in  the 
mouse  and  rabbit. 


Fig.  58. — Elbm 

Spleen.  X  560.  i.  Color- 
less blood  cells  2.  Epitheli.il 
cells.  3.  Colored  blood-corpus- 
cles. 4.  Cells  ■  _ 
ule.s :  the  upper  one  enclosing 
also  a  blood -corpuscle,  b. 
Techn.  No.  49. 


X  560, 
the  edge  ot  a  shake 
tion.    Techn.  No.  51 


X  s6o.  1  he  fi 
iblc  with  this 
Techn.  No.  52. 


The  Malpighian  corpuscles  are  usually  situated  in  the  forks  of  the  smaller 
arteries,  and  in  such  wise  that  the  artery  pierces  them  through  the  center  or  near 
the  periphery.  In  their  minute  structure  they  agree  entirely  with  the  secondary 
nodules  of  the  lymph-nodes,  and  occasionally  even  contain  germinal  centers. 


...  Surface  blackened  by  silv 


Malpighian  corpuscle. 


3.  61. — Section  of  Splbfn  of  Mouse,  Magnifi 
artery  The  sheath  of  the  artery  is  infiltrated  its 
the  pulp  and  the  artery  is  indicated  by  a  dotted  hi 


85  Times,  showing  the  ne 
:nt!re  length  by  lymphoid  ( 
Techn.  No.  54. 


The  Malpighian  corpuscles  are  also  temporary  structures,  continually  disin- 
tegrating and  developing  anew. 

The  spleen  pulp  forms  a  network  of  cords  which,  like  that  of  the  lymph- 
nodes,    occupies  the  interstices  of  the    trabecular    framework.      Occasionally 


THE    LYMPHATIC    SYSTEM. 


99 


the  cords  are  attached  to  the  Malpighian  corpuscles.     The  spleen  piilp  is  com- 
posed of  a  delicate  connective-tissue  reticulum  and  numerous  cellular  elements. 


Venous  capillarie 
(•■imermediat 
lacuna;"  ofothc; 
authors). 


Splenic  pulp. 


Fig.  62,  A. — Section 


Cat.    Techn.  No.  53- 


The  latter  are  in  part  leucocytes,  in  part  slightly  larger  nucleated  cells  ;  also  cells 
containing  colored  blood-corpuscles  and  free  colored  blood-corpuscles.  Pig- 
ment-granules are  also  present. 


Transition  of  venous 
capillaries  into — 


Flc.  62,  B.— Schematic  Drawing  op  Section  62,  A. 


The  Blood-vessels. — The  arteries  of  the  spleen  give  off  branches  to  the 
trabecule  and  to  the  pulp,  and  contribute   to  the  dense  capillary  network  of 


loo  HISTOLOGY. 

the  jMalpighian  corpuscles.  The  veins  proceed  from  a  wide-meshed  network 
of  capillaries  (venous  spaces,  venous  capillaries)  occupying  the  intervals 
between  the  trabeculse  and  the  pulp  cords  (Fig.  62).  The  larger  veins 
run  alongside  the  arteries.  The  precise  mode  of  communication  between  the 
arteries  and  the  veins  is  not  yet  determined.  The  arteries  break  up  into 
slender  capillaries  which  do  not  anastomose  with  one  another.  According  to 
one  view,  these  arterial  capillaries  are  directly  continuous  with  the  "venous" 
capillaries,  and  the  blood-vessels  are  closed  on  all  sides.  Other  authors  hold 
that  the  arterial  capillaries  pass  into  spaces  without  definite  walls,  "  inter- 
mediate lacunae,"  which  connect  with  veins  with  perforated  sieve-like  coats, 
and  that  the  latter  establish  the  communication  with  the  veins  with  closed 
walls. 

The  superficial  lymphatics  on  the  surface  of  the  spleen,  numerous  in  the 
lower  mammals,  are  scantily  developed  in  man.  The  deep  lymphatics  in  the 
interior  of  the  spleen  are  also  .few  in  number  ;  the  exact  relations  of  the  latter 
have  not  yet  been  fully  investigated. 

The  nerves,  which  comprise  a  few  meduUated  fibers  and  many  naked  axis- 
cylinders,  follow  the  course  of  the  trunks  and  branches  of  the  arteries,  supply- 
ing the  muscular  coats  of  the  latter,  and  in  the  lower  mammals  the  smooth 
muscle-fibers  of  the  trabecule  (Fig.  61).  Plexuses  of  nonmedullated  nerve- 
fibers  occur  in  the  spleen  pulp,  partly  sensory  in  their  nature,  and  probably 
proceed  from  the  branches  of  the  medullated  nerve-fibers  just  mentioned. 


111.   THE  ORGANS  OF  THE  SKELETAL  SYSTEM. 

The  skeletal  system  consists  of  a  large  number  of  hard  parts,  the  bones, 
which  are  joined  together  by  special  structures  and  form  in  their  entirety  the 
skeleton. 

In  the  embryo  the  greater  part  of  the  skeleton  consists  of  cartilage,  which 
in  the  course  of  development  is  supplanted  by  bone,  and  with  the  exception  of 
a  few  remnants  disappears  ;  such  remnants  are  the  costal  cartilages  and  the 
cartilages  of  the  joints,  which  cover  the  opposed  surfaces  of  many  bones. 
Skeletal  cartilages  are  also  found  in  the  respiratory  passages  and  the  organs 
of  special  sense. 

THE  BONES. 
On  sawing  through  a  fresh  long  bone,  it  will  be  seen  at  once  that  its 
texture  is  not  everywhere  alike,  but  that  the  osseous  tissue  appears  in  two 
forms:  the  one,  a  dense,  firm,  apparently  structureless  substance,  constitutes 
the  principal  portion  of  the  periphery  and  is  termed  compact  bone  (sub- 
stantia compacta)  ;  the  other,  toward  the  axial  cavity,  appears  as  an  irregular 


THE    HONES.  lOI 

reticulum  of  thin  osseous  lamella:  and  slender  trabeculfe,  and  is  called  s/iongy 
bone  (substantia  spongiosa).  The  interstices  of  the  spongy  bone,  as  well  as  the 
central  marrow-cavity,  are  filled  by  a  soft  mass,  the  hone-marrow ;  the  surface 
of  the  bone  is  enveloped  in  a  fibrous  membrane,  the  periosteum.  The  pro- 
portion between  the  compact  and  the  spongy  substance  is  different  in  the 
short  hones,  which  consist  chiefly  of  the  latter,  the  compact  substance  being 
limited  to  a  narrow  zone  at  the  periphery.  Flat  bones  have  sometimes  thicker, 
sometimes  thinner  outer  shells  or  crusts  of  compact  substance,  while  the  interior 
is  filled  with  spongy  substance.  In  the  epiphyses  of  the  long  bones,  as  in  the 
short  bones,  the  spongy  substance  preponderates. 


H.iversian  Can.iU. 


Fig.  63.— Piece  op  , 


LoNGiTUOiNAi.  Section  through  Human  Met 
canals.    At  x  Haversian  canals  open  on  the  outer. 


The  Spongy  siihsfance  consists  entirely  of  osseous  tissue ;  the  compact 
substance,  on  the  other  hand,  contains  besides  the  bone  canaliculi  and  lacunje, 
a  second  system  of  coarser  channels,  22  to  no  /x  wide,  which  divide 
dichotomously  and  form  a  wide-meshed  network.  These  channels  contain  the 
blood-vessels  and  are  named  Haversian  canals.  In  the  long  bones,  in  the  ribs, 
the  clavicle,  and  the  inferior  maxilla  their  course  is  parallel  to  the  long  axis  of 
the  bone;  in  short  bones  they  run  mainly  in  one  direction,  for  example, 
vertically  in  the  vertebra: ;  in  the  flat  bones  their  course  is  parallel  to  the  sur- 
face, not  infrequently  along  lines  that  radiate  from  a  point,  as  in  the  tuberosity 
of  the  parietal  bone.  The  Haversian  canals  open  on  the  outer  surface  of  the 
bone,  as  well  as  on  the  inner  surface,  directed  toward  the  substantia  spongiosa. 

The  ground-substance  or  matrix  of  bone  is  arranged  in  lamellae.  The 
fibrillte  are  joined  in  bundles,  and  these  placed  side  by  side  form  the  lamellse. 


I02  HISTOLOGY. 

According  to  the  disposition  of  these  strata  three  lamellar  systems  may  be 
distinguished  :  an  annular  or  Haversian  system,  in  which  in  cross-sections  eight 
to  fifteen  lamellae  are  seen  to  be  concentrically  arranged  around  an  Haversian 
canal;  these  lamellae  are  called  Haversian  or  special  lamella  (Fig.  64).  Between 
the  Haversian  systems,  which  come  into  contact  only  here  and  there,  are 
irregularly-disposed  lamellae,  the  interstitial  or  ground  lamella;  these  are  con- 
nected with  the  third  lamellar  system,  the  circumferential  or  fundamental 
lamellce,  in  which  the  osseous  strata  encircle  the  outer  and  inner  free  surfaces  of 
the  bone.  The  circumferential  lamellae  contain  a  variable  number  of  canals, 
which,  unlike  the  Haversian  canals,  are  not  the  centers  of  annular  systems  of 
lamellae;  they  are  called  Volkmann's  canals,  and  contain  the  "  perforating 
vessels."  The  latter  frequently  connect  with  the  vessels  of  the  Haversian 
canals ;  the  passage  of  the  Volkmann's  canals  into  the  latter  is  a  gradual  one. 
The  bone  lacuna  in  the  compact  substance  extend  in  a  definite  direction. 
In  the  Haversian  systems  their  long  axis  is  parallel   to  the  long  axis  of  the 


Haversian  canals,  and  they  are  bent  so  that  cut  transversely  in  the  cross-section 
of  an  Haversian  system  they  appear  concentrically  curved.  In  the  interstitial 
lamellae  the  lacunae  are  placed  irregularly  ;  in  the  circumferential  lamellae  so 
that  their  surfaces  extend  parallel  to  the  surfaces  of  the  lamellae.  The  bone 
canaliculi  open  into  the  Haversian  canals,  and  also  on  the  free  outer  and  inner 
surfaces  of  the  bone. 

The  bone-marrow  occupies  the  axial  cavity  of  the  tubular  bones,  fills  the 
interstices  of  the  spongy  substance,  and  is  also  found  in  the  larger  Haversian 
canals.  It  is  of  a  red  or  yellow  color,  and  therefore  two  varieties  are  recog- 
nized— the  red  marrow  and  the  yellow  marroto.  The  red  marrow  is  found  in 
the  vertebrae,  the  bones  of  the  skull,  the  sternum,  and  the  ribs — in  all  young 
bones  (also  in  the  long  bones  of  some  animals)  ;  the  yellow  marrow  occurs  in 
the  short  and  the  long  bones  of  the  extremities.  In  old  and  in  sick  persons  the 
marrow  is  mucoid  and  reddish-yellow,  and  is  characterized  by  its  poverty  in  fat. 


THE    BONES. 


103 


The  elements  of  red  marrow  comprise  a  delicate  connective-tissue  retic- 
ulum which  supports  a  few  fat-cells,  larger  and  smaller  marrow-cells,  and 
giant-cells  (myeloplaxes).  In  the  larger  marrow  spaces  the  connective  tissue 
forms  a  membrane,  the  endosteum,  which  lines  the  free  surface.  The  marrow- 
cells  exhibit  forms  resembling  leucocytes  ;  the  giant-cells  are  structural  anom- 
alies representing  leucocytes  enlarged  and  altered  in  form  ;    they  are  huge, 


1.. ;  Hematoblasts. 

\      (*/ 

(     Colored  blood-corpuscle. 

---  Giant-cell. 

Fig.  65. — Elements  OF  Human  Bone.Marrow.     X600:  1-5.  Various  forms  of  bone-cells.    6.  Eosinophilous 
cell.     Techn.  No.  57  b. 

extremely  irregular,  multinucleated  masses  of  protoplasm.  The  shape  of  the 
nucleus  varies  greatly  ;  it  may  be  round,  lobulated,  band-  or  hoop-shaped,  or 
it  may  fashion  a  network.  A  uninuclear  giant-cell  may  become  multinuclear 
through  the  division  of  the  nucleus  by  constriction,  or  a  corresponding  part  of 
the  protoplasm  may  be  set  free  with  the  nucleus  and  the  result  is  a  uninuclear 
cell.      The  view  interpreting  these  indications  of  division  as  the  phenomena  of 


Outer  fundamental  la 


Sharpey's  fibc 


Interstitial  lamellsc 


o 


Fig.  66.— Piece 


CHriss-SttCTioN  OP  Frmur  OP  Adult  Man.     X  80.     Techn.  No.  56.     The  la 
be  recognized  by  the  disposition  ot  the  lacuna:. 


a  reversed  series  of  processes — the  merging  of  several  cells  into  one — has  very 
little  probability,  since  the  process  of  budding  has  been  observed  in  living 
cells.  There  are  also  found  in  the  red  marrow  nucleated  cells  with  yellow- 
colored  protoplasm  like  that  of  the  colored  blood-corpuscles ;  the.se  are  the 
hematoblasts  (  erythrohlasts)  (Fig.  65).  Yellow  pigment-granules  that  appear 
in  the  different  cells  are  regarded  as  the  remains  of  disintegrated  colored  blood- 
cor|)uscles. 


I04 


HISTOLOGY. 


The  yellow  marrow  consists  of  a  connective-tissue  reticulum  containing 
much  fat.  Marrow-cells  and  hematoblasts  in  yellow  marrow  are  found  only  in 
the  head  of  the  humerus  and  the  femur. 

The  periosteum  is  a  compact  connective-tissue  membrane,  in  which  two 
layers  can  be  distinguished.  The  outer  is  characterized  by  its  richness  in 
blood-vessels  and  forms  the  connection  with  adjacent  structures,  tendons, 
fascise,  etc.;  the  inner  layer  contains  few  blood-vessels,  but  is  rich  in  elastic 
fibers  and  spherical  or  spindle-shaped  connective-tissue  cells.  At  places  on  the 
inner  surface  a  layer  of  cubical  elements  may  be  found,  which  are  of  importance 
in  the  development  of  the  bone.  The  periosteum  is  sometimes  firmly,  some- 
times loosely  attached  to  the  bone  ;    the  attachment  is  secured  by  the  blood 


Harrow  (fat-cells). 
Blood-vessel. 
Section  thkough  Head  of  a  Metacarpus  <'F  Adult  Man.      X  50.    Techn.  No.  59. 


vessels  passing  to  and  from  the  bone  and  by  Sharpey's  fibers,  which  pierce  the 
circumferential  and  interstitial  lamellae  and  extend  in  all  directions  (Fig.  66  ). 
The  blood-vessels  of  the  bone,  the  marrow,  and  the  periosteum  are  in  the 
closest  connection  with  one  another,  and  also  with  surrounding  structures. 
Small  branches  (not  capillaries)  of  the  numerous  arteries  and  veins  of  the 
periosteum  enter  the  Haversian  and  Volkmann's  canals,  and  on  the  inner 
surface  of  the  bone  are  in  communication  with  the  blood-vessels  of  the  marrow. 
The  latter  is  supplied  by  the  nutrient  artery,  which  in  its  course  through  the 
compact  substance  gives  off  branches  to  the  same,  and  in  the  marrow  breaks  up 
into  a  rich  capillary  network.     The  veins  that  take  up  the  capillaries  of  the 


THE    BONES.  I05 

marrow  have  no  valves.      Lymph-vessels  with  well-defined  walls  occur  only  in 
the  superficial  layer  of  the  periosteum. 

The  nerves  are  numerous  and  consist  partly  of  medullated,  partly  of  gray 
fibers.  They  enter  the  Haversian  canals  and  are  distributed  to  the  bone-mar- 
row and  the  periosteum,  and  in  the  latter  occasionally  terminate  in  Pacinian 
corpuscles. 

The  Articul.ations  of  Bones. 

Two  forms  of  articulations  are  recognized:  synarthroses,  joints  character- 
ized by  immobility;  diarthroses,  joints  in  which  the  bones  are  movable,  one 
upon  the  other. 

In  synarthroses  the  bones  are  joined  either  by  ligaments,  the  union  consti- 
tuting a  synifesmosis ;  or  by  the  intervention  of  cartilage,  forming  a  synchon- 
drosis. 

The  ligaments  are  fibrous  bands  possessing  a  structure  like  that  of  tendon, 
or  they  are  composed  of  elastic  tissue.  The  latter  are  distinguished  by  the 
possession  of  numerous  robust  elastic  fibers  which  are  never  arranged  in  bun- 
dles or  lamellse,  but  are  always  separated  by  loose  connective  tissue.  The 
ligamentum  nuchse,  ligamenta  subflava,  and  ligamentum  stylohyoideum  are 
elastic  ligaments. 

The  sutures  also  belong  to  the  syndesmoses  ;  short  fibrous  ligaments 
extend  from  one  serrated  osseous  edge  to  the  other. 

The  cartilage  in  synchondroses  is  rarely  only  of  the  hyaline  variety,  but 
usually  is  in  part  fibro -cartilage  (especially  at  the  borders  in  contact  with  the 
bone)  and  in  part  hyaline,  in  which  the  cell  capsules  are  frequently  calcified. 

The  intervertebral  ligaments,  which  belong  to  the  synchondroses,  possess 
a  soft,  jelly-like  center,  the  "gelatinous  nucleus,"  which  contains  groups  of 
cartilage  cells  ;  it  is  the  remains  of  the  notochord,  the  embryonic  precursor  of 
the  vertebral  column.  At  the  periphery  of  the  intervertebral  ligaments  there 
is  a  narrow  tendinous  zone. 

In  diarthroses  the  parts  entering  into  a  joint  are  the  articular  ends  of 
the  bones,  the  capsular  ligament,  the  marginal  fibro-cartilages,  and  the  inter- 
articular  cartilages. 

'l"he  articular  ends  of  the  bones  are  from  0.2-5  mm.  thick  and  are  covered 
by  a  stratum  of  cartilage  thinning  out  at  the  edges.  The  superficial  cartilage 
cells  are  flattened  and  placed  parallel  to  the  surface  ;  those  in  the  median  plane 
are  rounded  and  are  often  collected  in  groups  ;  in  the  deepest  plane,  the  groups 
of  cells  are  partly  arranged  in  longitudinal  rows,  vertical  to  the  surface  of  the 
cartilage  ;  adjoining  this,  but  separated  by  a  narrow  striated  belt,  is  a  small 
zone  of  calcified  cartilage  interjiosed  between  and  connecting  the  hyaline  car- 
tilage with  the  osseous  tissue  (  Fig.  67).  Not  all  the  articular  cartilages  ex- 
hibit the  same  structure;  the  cartilages  of  the  costo-vertebral,  the  sterno-clavi- 
cular,  the  acromio-clavicular,  and  the  maxillary  articulations,  and  the  head  of 
the  ulna  are  not  hyaline,  but  fibro-cartilage ;  the  distal  articular  surface  of  the 
radius  is  covered  with  dense  fibrous  tissue. 


io6 


HISTOLOGY. 


The  glenoid  ligament  and  the  interarticular  cartilages  do  not  exhibit  the 
characteristic  cartilage  matrix,  but  consist  of  a  compact  fibrous  connective 
tissue  and  of  spherical  cells.  To  the  same  category  belong  the  so-called  sesa- 
moid cartilages;  that  of  the  tendon  of  the  peroneus  longus,  however,  contains 
genuine  cartilage. 

In  the  adult,  nerves  and  blood-vessels  are  wanting  in  the  articular  carti- 
lages, as  also  in  the  interarticular  cartilages  and  the  glenoid  cartilage. 

The  capsular  ligaments  consist  of  an  external  fibrous  membrane,  K\\%  fibrous 
capsule,  of  varying  thickness,  possessing  a  structure  like  that  of  the  ligaments, 
and  of  an  internal  membrane,  the  synovial  membrane,  the  free  inner  surface  of 
which  is  smooth  and  glossy  ;  the  outer  layer  of  the  latter  is  composed  of  loose 
elastic  fibers  and  fibrillar  tissue  containing  fat-cells;  within  this  is  a  thin 
lamella  of  parallel  connective-tissue  bundles,  in 
which,  toward  the  interior,  there  are  spherical  or 
stellate  nucleated  cells,  11-17  ,a  in  size;'  they  are 
not  numerous  except  at  points  subjected  to  great 
pressure,  where  they  occur  in  large  numbers  and 
form  an  endothelial  membrane  three  or  four  strata 
thick. 

The  synovial  membranes  often  send  free  pro- 
cesses containing  fat  into  the  synovial  cavity,  and 
bear  on  their  free  surfaces  the  synovial  fringes  or 
villi,  variously  shaped  processes,  mostly  of  micro- 
scopic size,  which  closely  beset  the  edges  of  the 
joint  surfaces,  and  bestow  upon  the  synovial  mem- 
brane a  reddish,  velvety  appearance.  They  consist 
of  connective  tissue  and  are  clothed  by  a  single  or 
a  double  layer  of  cells. 

The  larger  blood-vessels  of  the  synovial  mem- 
branes lie  in  the  loose  connective-tissue  layer ;  the 
capillaries  extend  through  the  inner  thin  connec- 
tive-tissue stratum  and  form  vascular  tufts  in  the 
villi.  Some  of  the  villi  are  without  vessels.  The 
lymph-vessels  lie  close  under  the  endothelium. 

The  nerves  run  in  the  loose  connective  tissue  and  terminate  in  part  in 
Pacinian  corpuscles. 

The  synovia  consists  principally  of  water  ;  it  contains  only  six  per  cent. 
of  solids  and  no  formed  elements. 


Fig.   68,— SY^ 

JOVIAL    Villi    v 

^MTH 

Blood -Vbs: 

SELS     FKOM      Hu 

MAN 

Knee-Jo.ni 

•.  Magnified  f;o  ti 

mes 

Theepitheh 

urn  has  fallen  fror 

nthe 

apex  of  ihe 

left  villus.  ex-p( 

jsine 

theconnecti' 

^■e  tissue.   Techn 

.No 

The  Cartilages. 
The  costal  cartilages  are  of  the  hyaline  variety  ;  the  matrix  exhibits  the 
usual  characteristics  ;  the  cells  frequently  contain  fat.     The  surface  is   envel- 
oped by  a  compact   fibrous  membrane,  the  perichondrium,  which  consists  of 
interlacing  fibrous  bundles  and  elastic  fibers. 


THE    BONES. 


107 


The  articular  cartilages  are  covered  by  the  perichondrium  only  at  their 
edges,  not  on  their  free  surface.  Where  the  cartilage  and  the  perichondrium 
are  in  contact  there  is  a  gradual  transition  of  the  one  tissue  into  the  other,  and 
consequently  the  attachment  between  the  two  is  very  firm. 

The  perichondrium  carries  the  nerves  and  the  blood-vessels;  the  latter  also 
run  in  canals  within  growing  cartilage.  In  the  adult,  cartilage  is  devoid  of 
blood-vessels  ;  the  nutrition  of  the  tissue  depends  upon  diffusion  from  adjoining 
structures.  The  costal  cartilages  in  advanced  life  are  often  extensively  ossified 
and  contain  blood-vessels. 

The  cartilages  of  the  special-sense  and  the  respiratory  organs  will  be 
described  in  the  corresponding  chapters. 


Usteogenetic  tissue. 
Perichondnil  bone. 


::.  69. — Khom  a  Dokso-Plantar  Longitudinal  Section  op  Grbat  Ton  op  Fouk-Months'  Human  Em- 
BKVt).  TwO'thirds  of  the  first  ph;tlaiix  represented.  X  50.  i.  Lnctinae  enhirged  ntid  containing  many  carli- 
laeC'Cells,  I'hc  cells  cannot  be  distinguished  with  this  magnification,  only  their  nuclei,  which  appear  as 
minute  dots.  At  2,  developing  cartilage :  cells  in  groups  of  three  and  four,  each  group  produced  by  re- 
peated division  from  one  cartilage.cell.     Techn,  No.  61. 


Development  of  Bone. 
The  bones  are  comparatively  late  structures  in  their  appearance.  The 
development  of  the  muscles,  nerves,  blood-vessels,  brain,  spinal  cord,  etc.,  is 
alreaily  well  advanced  in  the  embryo  at  a  time  when  not  a  trace  of  bone  is 
present.  M  that  period  the  skeleton  is  formed  of  hyaline  cartilage.  With  the 
exception  of  certain  parts  of  the  cranium  and  nearly  all  the  bones  of  the  face, 
the  entire  skeleton  is  mapjied  out  in  cartilage.  In  the  upper  e.xtremity,  for 
example,  the  humerus,  radius,  ulna,  carpus,  and  the  skeletal  jjarts  of  the  hand, 
consist  of  cartilaginous  pieces,  which,  however,  are  not  hollow  like  the  bones 
by  which  they  are  subsequently  rejilaced,  but   are  solid   throughout.      The 


io8 


HISTOLOGY. 


osseous  skeleton  then  gradually  appears  in  the  place  of  the  cartilaginous.  All 
the  osseous  parts  that  in  the  embryo  were  preceded  by  cartilage  are  called 
primary  or  endochondral  bone  :  all  other  bones,  not  preformed  in  cartilage, 
secondary  or  interinenihranous  bone. 

The  primary  bones  include  all  the  bones  of  the  trunk  and  extremity,  the 
greater  part  of  the  cranium  (the  occipital  bone  with  the  exception  of  the  upper 
portion  of  the  tabular  part,  the  sphenoid  with  the  exception  of  the  internal 
pterygoid  plate,  the  temporal  bone  with  the  exception  of  the  squamous  portion 
and  the  annulus  tympanicus,  the  ossicles  of  the  ear,  the  ethmoid  bone,  the 
inferior  turbinal),  and  the  hyoid. 

The  secondary  bone  includes  the  bones  forming  the  sides  and  vertex  of 
the  cranium  and  nearlv  all  the  bones  of  the  face. 


Osteogenet 
Endochondral  bone 


Blood-vessels. 
Perichondral  bone. 


Enlarged  I 


Perichondral  bon 


Fig.  70.— From  a  Dorso-Palmar  Loncitudinal  Section  of  Kingkk  of  Four-Months'  Human  Embr 
Tu'o-thirds  of  second  phalanx  represented.  X  50-  'A'he  calcified  trabeculae  are  covered  by  a  thin  laye 
endochondral  bone.     (More  highly  magnified  in  Fig.  71.)     Techn.  No.  61. 


Development  of  Prim.^rv  Bone. 

Two  modes  of  bone  formation  are  here  to  be  considered:  i,  endochon- 
dral ossification,  formation  of  osseous  tissue  within  the  cartilage,  and  2,  perios- 
teal (better  perichondral )  ossification,  formation  of  osseous  tissue  immediately 
surrounding  and  also  on  the  cartilage.  The  phylogenetically  older  perichon- 
dral ossification  usually  begins  earlier,  but  for  didactic  reasons  will  be  described 
subsequently  to  the  process  of  endochondral  formation. 

I.  Endochondral  Ossification. — The  first  indications  of  this  process 
consist  in  changes  at  certain  places  within  the  cartilage  ;  the  cells  enlarge  and 
divide,  so  that  several  lie  in  one  lacuna  ;  a  deposition  of  lime-salts  takes  place 
within  the  matrix,  in  consequence  of  which  it  becomes  granular  and  dull — it 


THE    BONES. 


& 


calcifies.  Such  places  may  be  recognized  with  the  unaided  eye,  and  are 
called  centers  of  ossification  (better,  centers  of  calcification).  The  portions 
of  the  cartilage  remote  from  the  centers  of  calcification  continue  to  grow  in 


Hyaline  cartil- 
age (cells  re. 
arranged  in 


thickness  and  length,  while  at  the  center  growth  ceases,  and  consequently  the 
cartilage  at  this  point  appears  constricted  (Fig.  69).  Meanwhile,  on  the 
surface  of  the  center  of  calcification,  a  tissue  rich  in  blood-vessels  and  young 


no  HISTOLOGY. 

cells — ostcogenetic  tissue,-^  his  made  its  appearance.  This  penetrates  into  the 
cartilage,  the  calcified  matrix  is  absorbed,  the  cartilage-cells  are  set  free  and 
disintegrate;  a  little  space — \\\t.  primary  marrow-cavity — is  excavated  in  the 
center  of  calcification. 

These  processes  are  repeated  in  the  immediately  surrounding  cartilage; 
that  is,  the  matrix  calcifies,  the  cartilage-cells  enlarge,  new  portions  of  the  car- 
tilage break  down,  and  as  a  result  the  primary  marrow-space  is  gradually  and 
continuously  extended.  At  the  same  time  the  capsules  of  many  cartilage- 
cells  are  opened,  the  cells  degenerate,  and  the  intervening  calcified  matrix  pro- 
jects into  the  marrow-space  in  the  form  of  irregular  processes  or  trabeculre. 


Fig.  72.— Ck 


//.  Developing  H, 


The  primary  marrow-cavity  is  now  filled  with  blood-vessels  and  young  cells. 
The  fate  of  these  cells  in  the  further  course  of  development  varies.  They  retain 
their  original  form  and  become  marrow-cells,  or  they  become  fat-cells,  or — 
most  important — they  become  bone-forming  cells,  osteoblasts.  In  the  latter 
event,  a  number  of  cells  arrange  themselves  in  a  single  layer  on  the  walls  of  the 
marrow-cavity  and  on  the  surface  of  the  calcified  trabecule,  and  produce  the 
matrix  of  true  osseous  tissue. 

As  a  result  of  this  activity,  the  trabeculee  and  the  walls  of  the  marrow- 


*  This  is  not  a  good  name,  inasmuch  as  the  tissue  has  not  orig 
become  bone. 


lated  from  bone,  but  is  to 


THE    HONES.  Ill 

cavity  are  soon  covered  with  a  thin  layer  of  bone-substance,  which  gradually 
increases  in  thickness.  Thus  step  by  step  the  former  solid  cartilage  is  trans- 
formed into  spongy  bone,  the  trabeculas  of  which  still  contain  a  residue  of  cal- 
cified matrix  (Fig.  72). 

2.  Perichondral  Ossification. — This  mode  of  bone  formation  is  also  ac- 
complished through  the  agency  of  the  osteoblasts  derived  from  the  osteogenetic 
tissue  at  the  surface  of  the  center  of  calcification  ;  they  form  strata  of  spongy 
osseous  tissue  on  the  surface  of  the  cartilage,  which  is  distinguished  from  the 
endochondral  bone  in  the  absence  of  remnants  of  calcified  cartilaginous  matri.x, 
because  the  perichondral  bone  is  formed  at  the  circumference  and  not  in  the 
interior  of  the  cartilage.  The  formation  of  the  first  Haversian  canals  may  be 
observed  in  the  perichondral  bone  (Fig.  72).  The  latter  is  not  formed  in  a  con- 
tinuous layer  of  uniform  thickness,  but  at  frequent  intervals  depressions  or 
recesses  may  be  observed  containing  blood-vessels  surrounded  by  osteoblasts 
(Fig.  72  hit)  ;  at  first  the  recesses  are  open  toward  the  periphery,  but  with  the 
advancing  development  of  the  osseous  strata  they  are  closed  in,  and  then  rep- 
resent Haversian  canals.  The  osteoblasts  enclosed  within  the  canals  produce 
new  osseous  strata,  the  Haversian  lamells. 


1  '->;!. 

Carlilagc-cell. 


Transitional  form  of  a  cartilage- 
cell  undergoing  conversion  into 


Dug.      X  240-     Metaplastic  type. 

By  the  absorption  of  the  cartilage  and  its  substitution  by  o.sseous  tissue, 
also  by  the  deposition  of  bone-substance  on  its  e.Kterior,  the  piece  of  cartilage 
has  become  a  bone. 

The  essence  of  the  foregoing  processes  consists  in  an  absorption  of  the 
parts  of  the  primordial  skeleton  and  in  the  new  formation  of  the  same  by  the 
development  of  bone-substance.  This  mode  of  bone  formation  is  termed  neo- 
plastic in  contradistinction  to  the  rarer  vietaplastic  mode,  in  which  the  cartilage 
is  not  destroyed  but  ossified,  and  the  cartilage  matrix  becomes  the  bone  matrix, 
the  cartilage-cells  the  bone-cells  (as  for  example,  in  the  angle  of  the  inferior 
maxilla)  (Fig.  73). 

Secondary  or  Interme.mbranocs  Bone. 
In  this  the  fundament  on  which  the  forniation  of  bone  occurs  is  not  carti- 
lage but  connective  tissue.     Isolated  bundles  of  connective  ti.ssue  calcify ;  on 
these  osteolilasts  derived  from  embryonal  cells  arrange  themselves  and  produce 
bone,   in    the   manner   above   described    (Fig.    74).     The    intermembranous 


HISTOLOGY. 


;-tissue  bundles. 


bone  is  enclosed  on  all  sides  by  connective  tissue  :  when  osseous  tissue  is  in 
direct  contact  on  one  side  with  cartilage,  without  the  intervention  of  con- 
nective tissue,  the  resulting  formation  is  not  intermembranous,  but  perichon- 
dral bone. 

Growth  of  Bone. — In  tubular  bones  ossification  in  the  diaphysis  begins 
much  earlier  than  in  the  epiphyses  (\\\  the  humerus  the  center  of  ossification 
in  the  diaphysis  appears  in  the  eighth  fetal  week,  in  the  epiphyses  in  the  first 

year  of  life)  ;  blood-vessels  grow  into 
the  calcified  cartilage  which  is  trans- 
formed at  first  by  endochondral,  later 
by  perichondral,  formation  into  bone. 
The  articular  surfaces  of  the  bone  re- 
main permanently  cartilaginous  ;  and 
a  narrow  zone  between  the  diaphysis 
and  each  epiphysis,  the  epiphyseal  carti- 
lage, persists  until  the  growth  of  the 
bone  is  completed.  An  active  growth 
of  cartilage  is  maintained  here,  which 
by  e-\tension  of  the  primary  marrow-cavities  of  the  diaphysis  and  the  epiphyses 
is  continually  being  supplanted  by  bone.  In  this  way  the  bone  grows  in 
length.  Increase  in  thickness  takes  place  by  the  "apposition"  of  new  peri- 
osteal strata. 

In  the  short  bones  ossification  takes  place,  as  in  the  epiphyses,  at  first  by 
endochondral  formation  ;  after  the  absorption  of  the  superficial  remnant  of 
cartilage,  a  perichondral  osseous  shell  is  formed. 

In  they?ir/  bones  perichondral  precedes  endochondral  formation. 
Intermembranous  bones  grow  in  superficies  and  thickness  by  the  formation 
of  new   osseous  masses  at    their   edges 
and  their  surfaces  respectively.     As   a        '"' 
consequence  of  the  abundant  deposition 
of   bone-substance  on  the   surface,   the 
outer  and   the  inner  tables  of  compact    Bone 
bone  are  formed,  which  enclose  between         /, 
them  spongy  bone  ;  the  latter  is  termed 
diploe  in  this  situation.     The  osseous 
masses  at  first  possess  a  coarse-fibered, 
and  later  (from  about  the  first  year  of       ^^\ 
life)  a  fine-fibered  matrix. 

Re.sorption  of  Bone. — Immedi- 
ately following  the  initial  formation  of  osseous  tissue  a  contrary  process, 
resorption,  becomes  perceptible,  by  which  the  calcified  cartilage  matrix  and 
many  parts  of  the  primary  or  endochondral  bone  are  removed.  Resorption  is 
actively  carried  on  in  the  tubular  bones  in  the  formation  of  the  marrow-spaces 
(in  a  lesser  degree  in  other  bones)  and  on  the  surface  of  bones  until  their 
tyi)ical  form  is  completed.     The  femur  of  a  three-year-old  child,  for  example. 


ells  lying  in  Howship's  lacunx. 


—From  a  Cross-Section  of  Humerus 
Newborn  Cat.  X  240.  H.  Haver- 
pace,   containing   two   blood-vessels   and 


THE   ORGANS    OF   THE    MUSCULAR    SYSTEM. 


"3 


contains  scarcely  any  of  the  osseous  tissue  present  at  birth.  In  the  interior 
of  the  compact  bone  irregular  excavations  may  be  seen,  the  so-called 
Haversian  spaces,  formed  by  the  absorption  of  the  innermost  Haversian 
lamellae,  which,  however,  may  be  partly  filled  again  by  the  deposition  of  new- 
osseous  substance. 

Wherever  resorption  of  bone  takes  place,  multinucleated  giant-cells  may 
be  seen  lying  in  depressions  or  pits — ffawship's  lacuna — which  they  have 
excavated  in  the  bone.  In  this  situation  the  giant-cells  bear  the  name  of 
osteoclasts  (Fig.  75). 

Even  in  the  fully-developed  skeleton  the  processes  of  apposition  and 
resorption  still  occur  at  isolated  places. 


IV.  THE  ORGANS  OF  THE  MUSCULAR  SYSTEM. 


y 


The  muscular  system  is  composed  of  a  large  number  of  contractile  organs, 
the  muscles,  which  consist  of  cross-striated  muscle-tissue  and  are  joined  to  the 
skeleton,  the  skin,  the  viscera,  etc., 

by   the   intervention  of  special   con-  ^w^    ' 

nective-tissue  formations,  the /.fWf/c/w,  ■     ^ 

and  accessory  parts  of  similar  struc- 
ture,   the  fascia,   tendon-sheaths,  and  ^  - 
bursa.                                                                 „ 

Each  muscle  is  composed  of 
striated  muscle-fibers  which,  as  a  rule, 
are  disposed  parallel  and  lengthwise 
in  bundles  surrounded  by  a  connective- 
tissue  sheath,  tht  perimysium. 

Interlacing  is  rare,  but  occurs, 
for  example,  in  the  tongue.  Neigh- 
boring muscle-fibers  are  never  in  direct 
contact,  but  each  individual  fiber  is 
enveloped  in  a  delicate  connective- 
tissue  sheath,  the  endomysium,  which 
is  joined  to  neighboring  sheaths  (Fig. 
76).  A  number  of  muscle  bundles 
form  a  muscle,  the  surface  of  which  is 
covered  by  a  robust  connective-tissue 
membrane,  the  epimysium.  The  sev- 
eral sheaths  are  connected  with  one  another.  The  grouping  of  the  primary 
bundles  into  secondary  bundles,  which  in.  a  certain  number  of  instances  are 
grouped  into  tertiary  bundles,  and  finally  united  to  form  a  muscle,  is  an  arbi- 
trary division,  and  in  many  preparations  cannot  be  recognized. 


"0" 


Fig.  76. — From  a  Cross-Section  ..f  the  Adductor 
MfscLE  OF  A  Rabbit.  P.  Fcrimysium,  conuining 
two  blood-vessels,  at  ^  ;  m,  muscle-fibers ;  many  are 
shrunken  and  between  them  the  endomysium,  /,  can 
be  seen ;  at  x  the  section  of  muscle-fiber  has  fallen 
out.     X  60.    Techn.  No.  tt. 


114 


HISTOLOGY. 


The  perimysium  is  composed  of  fibrillar  connective  tissue  and  numerous 
fine  elastic  fibers,  and  occasionally  contains  fat-cells  ;  it  conveys  the  nerves 
and  lymph- vessels.  The  endomysium  contains  only  capillaries  and  terminal 
branches  of  nerves. 

The  post-embryonal  increase  in  the  thickness  of  the  muscle  depends  less 
on  the  division  than  on  the  growth  in  thickness  of  the  already  existing  muscle- 
fibers. 

The  tendons  are  characterized  by  the  parallel  course  of  their  fibers,  their 
firm  union,  and  the  scarcity  of  elastic  fibers.  They  are  composed  of  bundles 
of  fibrous  tissue,  the  primary  or  tendon-bundles,  which  are  held  together  by 
looser  connective  tissue  and  form  secondary  bundles.  Each  primary  bundle 
consists  of  a  number  of  parallel  fibrillae,  running  a  straight  course  and  united 
by  a  small  amount  of  cement-substance.     Between  the  primary  bundles  lie  the 


Tendon-bundk.     


Fig.  77. — A.  From  a  Cross-Sbction  of  Dried  Tendon  of  Adult  Man.    X  50.    Techn.  No.  63.     B.  From 
a  cross-section  of  tendon  fixed  with  chromic  acid  (adult  man).     Tcchn.  No.  64. 


cellular  elements  of  the  tendon,  fusiform,  stellate,  polygonal,  or  flat  cells, 
arranged  in  longitudinal  rows.  They  partially  clasp  the  primary  bundles  and 
unite  with  one  another  by  means  of  processes.  Elastic  fibers  are  found  chiefly 
in  the  loose  connective  tissue ;  in  the  dense  tendon-bundles  they  are  scarce 
and  occur  in  the  form  of  a  fine  wide-meshed  network. 

The  union  of  muscles  with  tendons  and  fibrous  membranes  is  effected  by 
the  extension  of  the  endomysium  of  the  muscle-fiber  to  these  structures,  and 
the  blending  of  the  tissues ;  the  sarcolemma  takes  no  part  in  this,  but  as  a  con- 
tinuous sheath,  with  pointed  or  obliquely  blunted  ends,  closely  invests  the  mus- 
cle-fibers. When  the  muscle-fibers  are  spread  out  in  a  membrane  they  attach 
themselves  to  the  connective  tissue  ,by  pointed  or  forked  ends. 

'X\\^  fascia  in  part  exhibit  the  same  structure  as  the  tendons,  and  in  part 
they  are  fibrous  membranes  richly  provided  with  elastic  fibers.     The   latter  is 


THE    ORGANS    OF    THE    MUSCULAR    SYSTEM. 


"5 


the  case  where  they  form  sheaths  for  the  muscles  and  do  not  furnish  surfaces 
for  the  attachment  of  the  muscle-fibers. 

The  tendon-sheaths  and  the  biirsce  consist  of  a  layer  of  connective  tissue  and 
elastic  fibers,  varying  in  thickness,  the  inner  surface  of  which  is  covered  patch- 
wise  by  polygonal  endothelial  cells.  Where  the  endothelium  is  wanting  the 
connective  tissue  is  dense  and  rich  in  rounded  elements  resembling  cartilage- 
cells.  The  majority  of  the  tendon-sheaths  have  small  vascular  processes  exactly 
like  the  synovial  fringes. 

The  blood-vessels  of  striated  muscles  are  very  numerous  and  uniformly  dis- 
tributed ;  the  capillaries  are  among  the  thinnest  in  the  human  body,  and  form 
networks  characterized  by  elongated  rectangular  meshes,  closely  surrounding 
the  individual  fibers. 


Nucleus.  - 
Protoplasm.    — U 


-<^ 


Fig.  78. — Tendons  fkom  Rat's  Tail.  X  240.  A.  TenHon-ce! 
in  profile,  B,  from  the  surface.  At  X  the  nucleus  is  bent  so 
seen  partly  tn  profile  (the  shaded  portion)  and  partly  from  th 
(the  light  portion).    Tcchn.  No.  65. 


Muscle-/,       W/ 
fibers.^^-T'W^ 

11  viewed 
that  it  is 
e  surface 

Fig.  79.  —  From  a  Sagittal 
Longitudinal  Section  op 
THE  Gastrocnemius  OF  Frog. 

X  50  The  uppermost  trans- 
verse line  represents  the  endo- 
mysium  seen  from  the  surface. 
Techn.  No.  66. 

The  veins  are  provided  with  valves  throughout  their  course,  even  in  their 
smallest  branches.  The  lymph-vessels  are  few  in  number  and  follow  the 
branches  of  the  smaller  blood-vessels. 

For  the  nerves,  partly  sensory  and  partly  motor,  see  the  Peripheral  Nerve- 
Endings. 

The  blood-vessels  of  the  tendons  and  the  thinner  fascis  are  very  scarce, 
and  run  in  the  loose  tissue  between  the  fibrous  bundles  ;  the  tendon-sheaths,  on 
the  other  hand,  and  the  bursK  have  a  rich  vascular  supply.  Lymph-vessels  are 
found  only  on  the  surface  of  the  tendon. 

The  medullated  nerves  of  tendons  terminate  in  part  in  a  close  plexus  of 
gray  nerve-fibers,  and  in  part  in  tendon-spindles,  a  formation  resembling  the 
motorial  end-plates.  End-bulbs  and  Pacinian  corpuscles  also  are  found  in  ten- 
dons, fasciffi,  and  tendon-sheaths. 


V.  THE  ORGANS  OF  THE  NERVOUS  SYSTEM. 

I.  THE  CENTRAL  NERVOUS  SYSTEM.* 

THE  SPINAL  CORD. 

Topography. — The  spinal  cord  consists  of  a  white  and  a  gray  substance, 
distinguishable  by  the  unaided  eye.  The  arrangement  and  the  relation  of  these 
two  substances  are  best  recognized  in  cross-sections  of  the  spinal  cord. 

The  white  substance  encircles  the  gray  matter,  and  is  partially  divided 
by  a  deep  anterior  cleft,  the  anterior  median  fissure,  and  a  posterior  septum 
(formerly  called  the  posterior  median  fissure)  into  a  right  and  a  left  half.  Each 
half  is  subdivided  by  the  furrows  marking  the  exit  of  the  anterior  and  the 
posterior  roots  of  the  spinal  nerves  into  a  large  lateral  column,  an  anterior  col- 
umn, and  a  posterior  column.  In  the  lower  cervical  and  the  upper  thoracic 
regions  two  divisions  may  be  distinguished  in  the  posterior  column,  of  which  the 
median  portion  is  named  the  column  of  Goll  (funiculus  gracilis),  and  the  lateral 
portion  the  column  of  Burdach  (funiculus  cuneatus).  The  anterior  columns 
are  united  by  the  icihife  commissure  at  the  bottom  of  the  anterior  median 
fissure. 

The  gray  substance  appears  in  cross-section  in  the  form  of  an  H,  and 
consists  of  two  lateral  columns  or  masses  connected  by  a  horizontal  bridge,  the 
gray  commissure.  On  each  mass  thick  anterior  cornua  and  slender  posterior 
cornua  may  be  distinguished.  Adjoining  the  lateral  portions  of  the  anterior 
horns,  and  horizontally  even  with  the  central  canal,  are  the  lateral  cornua,  which 
are  especially  well-developed  in  the  upper  thoracic  region.  From  the  front 
boundary  of  the  anterior  cornua,  the  anterior  roots  of  the  spinal  tien'es  emerge 
in  several  bundles,  while  the  posterior  roots  enter  at  the  postero-median  side 
of  the  posterior  cornua.  At  the  base  of  the  posterior  cornua,  laterally,  a  net- 
like mass  of  gray  substance,  the  reticular  process,  is  found  ;  at  the  median  side, 
near  the  gray  commissure,  lies  the  well-defined  column  of  Clark  (dorsal 
nucleus),  visible  in  the  whole  length  of  the  thoracic  and  in  the  upper  part  of 
the  lumbar  regions  of  the  cord ;    and  capping  the  summit,  a  glistening,  jelly- 


*  I  shall  confine  myself  here  to  a  brief  account  of  the  topography  and  histology  of  the 
spinal  cord  and  the  brain.  An  exhaustive  presentation  of  the  architecture  of  the  central  nervous 
system,  the  paths  of  the  nerve-fibers,  and  the  complicated  origins  of  the  cranial  nerves  in  the 
"nuclei"  of  the  oblongata  would  exceed  the  limits  of  this  "Histology."  The  student  is 
referred  to  special  text-books,  of  which  Edinger's  "  Vorlesungen  iiber  den  Bau  der  nervSsen 
Centralorgane  "  is  recommended. 

Il6 


THE   CENTRAL   NERVOUS   SYSTEM. 


"7 


like  mass,  the  suhstantia  gelatinosa  Rolandi  may  be  distinguished.  Posteriorly 
to  this  is  the  small  zona  spongiosa,  at  the  dorsal  edge  of  which  is  found  the  zona 
termiiialis,  an  area  of  cross-sectioned  thin  nerve-fibers.  In  the  gray  commis- 
sure lies,  in  section,  the  central  canal,  which  extends  through  the  whole  length 
of  the  cord  and  is  surrounded  by  the  substantia  gelatinosa  centralis.  The  cen- 
tral canal  is  from  0.5  to  i  mm.  in  diameter;  not  infrequently  it  is  impervious. 
The  portions  of  the  gray  commissure  in  front  of  and  behind  the  canal  are 
named  respectively  the  anterior  znd  xhe.  posterior  gray  commissure.  From  all 
points  of  the  periphery  of  the  gray  substance  coarser  or  finer  processes,  the 
septula  meilullaria,  radiate   into   the    white  substance.    'In   the    cervical    and 


Lateral  posterior 

Mcdi.1l  anter 
Groups  of  ncrve-cclls. 


erior  median    Anterior  „„  .     ^ 
iissure,  column.   White  commissure. 


'  commi!  _  _. 
lich   is   the 
canal. 


Fig.  80. — Cross-Section  of  the  Cervical  Enlargement  of  the  Hvman  Spinal  Cord.    X  7. 

Techn    No    68 


the  lumbar  enlargements  of  the  cord  the  gray  matter  is  more  powerfully  devel- 
oped than  in  the  thoracic  region,  and  there  is  a  corresponding  variation  in  the 
form  of  the  H.  The  end  of  the  cord,  the  conns  mcdullaris,  consists  almost 
wholly  of  gray  substance. 

Minute  Structure. — The  gray  substance  will  be  first  considered,  a  knowl- 
edge of  its  composition  being  essential  to  the  comprehension  of  the  structure  of 
the  white  substance.  It  consists  of  multipolar  ganglion-cells,  which  with  their 
ramifying  and  axis-cylinder  processes  form  a  dense  nervous  tangle,  the  "  nerve- 
felt,"  which  is  penetrated  by  nerve-fibers  proceeding  in  part  from  the  white 
columns  and  in  part  from  the  posterior  roots,  and  the  whole  is  supported  by  a 
framework  of  neuroglia. 


ii8 


HISTOLOGY. 


The  iien<c-cells  are  divided  in  accordance  with  the  relations  of  their  axis- 
cylinder  processes  into  motor-cells  and  "column-cells  "  {Sfrangzellcn). 

The  moto?-  nerve-cells  lie  in  two  groups  in  the  anterior  horn,  an  antero- 
median and  postero-lateral,  separate  in  the  cervical  and  lumbar  enlargements, 
but  in  the  uppermost  cervical  and  in  the  thoracic  regions  united  in  a  single 
cluster  (Fig.  80).  In  longitudinal  sections  it  may  be  seen  (conspicuously  in 
amphibians)  that  the  cell  groups,  governed  by  the  origin  of  the  single  roots, 
have  a  correspondingly  typical  segmental  arrangement.  The  cells  possess  a 
large  cell-body  (67  to  135  /i)  and  long  protoplasmic  processes,  dendrites, 
extending  far  into  the  surrounding  substance  ;  the  nerve-  or  axis-cylinder 
process  emerges  from  the  summit  of  the  anterior  cornu,  makes  an  oblique 
descent  through  the  white  substance,  at  the  same  time  receives  a  medullary 
sheath,  and  becomes  the  axis-cylinder  of  a  medullated  nerve-fiber.  Occasion- 
ally the  axis-cylinder  process  gives  off  a  few  lateral  twigs  before  leaving  the 


Lateral  column-cell  with h'^'~ 


Motor-cell  of  the  latera 
posterior  group. 


Com  missural-cell . 


Fig.  81.— Cross-Section  of  thh  Spinal  Cord  of  a  Seven-Days'  Old  Embryo  Chick.     X  80. 
matter  is  but  slightly  developed,  the  central  canal  still  very  large.     Techn.  No.  70. 


gray  matter.  It  leaves  the  spinal  cord  as  a  part  of  the  anterior  root-fiber 
bundle.  All  anterior  root-fibers  arise  from  the  motor-cells  of  the  anterior 
horn,  and  on  the  same,  not  the  opposite,  side. 

The  column-cells  constitute  the  chief  mass  of  the  nerve-cells  of  the  gray 
substance,  and  lie  partly  scattered,  partly  grouped  in  the  lateral  horn  and  in 
the  dorsal  nucleus.  The  majority  are  smaller  than  the  motor  nerve-cells  and 
possess  fewer  and  less-branched,  but  far-reaching,  dendrites.  Their  axis- 
cylinder  process,  after  sending  off  numerous  collateral  fibrils  in  the  gray  sub- 
stance, enters  the  white  substance — the  anterior  or  the  lateral  columns,  very 
rarely  the  posterior — either  on  the  same  or  on  the  opposite  side ;  in  the  latter 
case  the  cells  are  sometimes  termed  commissure-cells,  because  the  axis-cylinder 
passes  through  the  anterior  gray  commissure  before  entering  the  white  sub- 
stance. The  commissure-cells  occupy  an  area  embracing  the  central  canal  in 
an  arch  on  the  ventral  side.     Having  arrived  in  the  white  substance,  the  axis- 


THE    CENTRAL    NERVOUS    SYSTEM. 


119 


cylinder  process  of  the  majority  of  the  column-cells  divides  into  a  vertical 
ascending  and  descending  "stem-fiber,"  which  in  its  course  parallel  to  the 
longitudinal  axis  of  the  spinal  cord  sends  off  lateral  twigs  (collateral  fibrils), 
which  return  to  the  gray  substance,  where  they  terminate  in  tufts  of  free  fibrils ; 
the  stem-fibers  themselves  finally  terminate  like  the  collateral  fibers.  The 
collateral  fibers  that  enter  into  the  anterior  columns  are  tolerably  robust  and 
penetrate  the  anterior  cornua  singly  or  in  bundles,  where  they  weave  a  net 
around  the  large  motor-cells;  they  are  especially  robust  in  the  antero-lateral 


Collateral  fibrils. 


Ascending  fiber. 


Spinal  ganglion-cell. 


Descending  fibe 


curve  of  the  anterior  horn.  Less  numerous  are  the  collateral  fibers  coming 
from  the  lateral  columns,  which  go  chiefly  to  the  substantia  gelatinosa  cen- 
tralis, and  only  those  ventral  to  the  substantia  gelatinosa  Rolandi  are  well 
developed  ;  the  latter  pass  to  the  opposite  side  and  form  the  dorsal  or  pos- 
terior commissure.  In  the  adult,  all  the  nerve-processes  of  the  column-cells  are 
enveloped  in  a  medullary  sheath.  The  axis-cylinder  processes  coming  from 
the  vesicular  column  of  Clarke  do  not  divide  in  the  white  substance,  but  turn 
craniaKvard  and  proceed  to  the  cerebellum.     The  axis-cylinder  processes  of 


I20  HISTOLOGY. 

Still  Other  column-cells,  arrived  in  the  white  substance,  turn,  without  divid- 
ing, upward  or  downward.  There  have  been  described,  under  the  name  of 
"  pluricordonal  "  cells,  elements  whose  axis-cylinder  processes  divide  into  two 
or  three  branches  and  continue  in  as  many  fibers  in  the  different  columns. 

The  cells  so  far  described  belong  to  the  nerve-cells  of  the  first  type  (Dei- 
ters's).  There  is  another  kind  of  cell,  whose  nerve-process  rapidly  divides, 
but  remains  within  the  gray  substance.  For  this  reason  these  elements  are 
termed  interior  cells  ;  they  occur  in  the  posterior  columns  and  are  nerve-cells  of 
the  second  type  (Fig.  84). 

The  nerve-fibers  that  enter  the  anterior  and  lateral  columns  arise  in  part 
from  the  medullated  collateral  fibers  and  the  ends  of  the  nerve-processes  of  the 
column-cells,  in  part  from  the  axis-cylinder  processes  (likewise  invested  by  a 
medullary  sheath)  that  come  from  the  brain.*     To  these  belong  the  medullated 

fibers  of  the  posterior  roots  which  origin- 
j  \\\  itt      ^'^  ^"   *^^  centripetal   processes  of  the 

Ascending  fiber. 1 yMf       ^^^^^  °'"  *^^  Spinal  ganglia.     These  poste- 

I  I uiiM       '''°''  toot-fibers  enter  the  spinal  cord  in 

'i/^^^^WAJAil       two  groups,  a  lateral  which  runs  in  the 

Descending  fiber. --^^^ss^--j^^u  11      ^oua    temiinalis,    and    a    median    which 

Nerve-fibers  of  pos-   ../'/Y/      !  'Af! /'''!         ri'^s    in    the    posterior    columns.       The 
tenor  root,     ^j^    ^  ,:       ^        fibers  do  not   enter  the  gray  substance 

'[.'■-.  directly,  but  each   first  divides  Y-shape 

'  into  an  ascending  and  a  descending  stem- 

fiber  (Fig.  83),  from  which  numerous  col- 
lateral fibers  diverge  at  right  angles ;  these 
now  enter  the  gray  substance,  and  with 
their  tufts  of  terminal  fibrils  distribute 

Longitudinal    Section   of 

Cord  of  a  Newborn  Rat.   X      themselvcs  over  nearlv  every  point  of  the 

:tion   shows  two  posterior    nerve-  -  ^    ^ 

roots.    The  collateral  fibrils  are  not  visible,      same :    One  Set  terminates  principally  in 

Techn.  No.  70.  r  i         ./ 

the  summit  of  the  posterior  horn  ;  these 
take  their  origin  in  the  lateral  root-fiber  group  and  form  a  very  fine-fibered 
dense  plexus,  that  partly  lies  in  the  substantia  gelatinosa  Rolandi  (Fig. 
84  c) ;  the  second  set  terminates  in  Clarke's  column  (Fig.  84  a)  ;  they 
originate  in  the  median  root-fiber  group,  as  also  a  third  set,  which  passes 
through  the  middle  of  the  substantia  gelatinosa  Rolandi  ventralward  into 
the  anterior  cornu,  and  there  radiates  fan-shape  and  surrounds  the  motor- 
cells  in  a  network  of  fibrils  (Fig.  84  F)  ;  the  latter  set  forms  the  reflex 
bundle.  This  and  the  collateral  fibers  of  Clarke's  column  sink  into  the  gray 
substance  in  a  curve  with  the  concavity  laterahvard,  and  form  a  conspicuous 
mass  easily  perceived.  There  are  other  collateral  fibers  which  pass  through  the 
posterior  gray  commissure  to  the  fibers  (the  so-called  "crossed")  of  the  opposite 
side.     The  stem-fibers,  probably  only  after  a  long  course  (several  centimeters), 

*  For  an  account  of  the  exact  course  of  these  fibers  the  student  is  referred  to  special  text- 
books. 


THE    CENTRAL    NERVOUS    SYSTEM.  121 

turn  into  the  gray  substance,  where  they  terminate  like  the  collateral  fibrils 
in  fine  branches. 

The  peculiarities  of  the  substantia  gelatinosa  centralis  and  Rolandi,  which 
belong  to  the  gray  substance,  are  dependent  upon  the  abundance  of  neur- 
oglia, and  will  be  described  with  this. 

The  white  substance  is  composed  entirely  of  meduUated  nerve-fibers 
which  are  without  the  sheath  of  Schwanrj.  The  fibers  differ  greatly  in  thick- 
ness ;  the  thickest  are  found  in  the  anterior  columns  and  in  the  lateral  parts  of 
the  posterior  columns  ;  the  thinnest  in  the  median  part  of  the  posterior  columns 
and  in  the  lateral  columns  where  the  white  and  the  gray  substances  touch.  In 
the  remaining  portions  thick  and  thin  fibers  are  intermingled.    The  majority  of 


Blood-vessels. 


Collateral  fibril  of  a  column-cell. 


Fig.  84.— Cross-Sbction  of  the  Spinal  Cord  of  a  Nbwborh  Rat  Showing  Collateral  Fibrils. 
In  the  right  half  only  one  representative  of  each  kind  has  been  sketched.     Techn.  No.  70. 


the  nerve-fibers  run  parallel  with  the  long  a.xis  ot  the  spinal  cord,  and  hence  in 
cross-sections  are  cut  transversely.  In  addition  there  are  fibers  that  take  an 
oblique  direction  ;  these  are  found  in  large  numbers  in  front  of  the  gray  com- 
missure, where  they  cross  at  acute  angles  and  form  the  white  commissure  (Fig. 
So). 

An  attempt  to  classify  the  nerve-fibers  according  to  their  origin  will 
result  as  follows  :  i,  fibers  w^hich  are  continuations  of  the  posterior  root ;  the 
entire  posterior  column  consists  of  posterior  root-fibers,  because  the  latter  (or 
their  stem-fibers),  entering  in  the  lumbar  region,  are  jnished  toward  the  median 
line  by  the  fibers  entering  at  higher  levels;  2,  fibers  which  are  continuations 
of  the  column-cells  ;   3,  fibers  which  are  continuations  of  the  ganglion-cells  of 


122  HISTOLOGY. 

the  brain.      Both  the  latter  occupy  the  anterior  and  the  lateral  columns  and  are 
united  in  compact  bundles  (funiculi). 

The  supporting  framework  of  the  spinal  cord  is  constructed  of  two  geneti- 
cally distinct  formations:  i,  fih7-ous  connective-tissue  extensions  of  the  pia, 
which  penetrate  the  white  substance  as  sheaths  for  the  blood-vessels  ;  this 
mesenchymal  framework  grows  constantly  thinner  as  it  approaches  the  gray 
substance,  into  which  it  does  not  extend  ;  2,  the  neuroglia  ("  nerve-cement ") 
which  is  derived  from  the  same  embryonic  anlage  as  the  central  nervous  system. 
The  neuroglia  consists  principally  of  nucleated  elements,  the  glia-cells, 
and,  possibly,  of  a  small  amount  of  homogeneous  ground-substance.  There 
are  two  kinds  of  glia-cells.     The  one  kind  are  the  ependymal  cells,  which  in  a 


wborn  rat. 
Glia-ccll. 


Ependymal  cells 


Fig.  85. — Glia-Cells  from 


Glia-cell  of  gray  matter  of  the  base  of  the 
posterior  horn  of  a  human  embryo. 

Spinal  Cord.     X  280.     Techn.  No.  70. 


single  layer  line  the  lumen  of  the  central  canal.  In  youth  they  are  beset  with 
cilia.  Their  cylindrical  bodies  are  prolonged  in  an  extended  process  which  in 
the  embryo  reaches  to  the  surface  of  the  spinal  cord,  where  it  terminates  in  a 
simple  or  branched  end  (Fig.  85).  The  cells  of  the  ependyma  are  phylo- 
genetically  the  older ;  they  arise  also  ontogenetically  first,  but  in  the  further 
course  of  development  undergo  retrogression  in  different  degrees,  which  not 
infrequently  leads  to  complete  obliteration  of  the  central  canal.  The  second 
kind  of  glia-cells  are  the  so-called  Deiters' s  cells,  which  in  the  beginning  of 
their  development  lie  in  the  gray  substance  ;  later  they  retreat  into  the  white 
substance,  and  then  assume  various  shapes.  Of  the  numerous  processes  of  these 
cells  one,  the  "chief  process,"  originates  first;  the  others,  partly  fine  and 
partly  coarser  "secondary"  processes,  later.      Many  of  these  cells,  with  their 


THE    CENTRAL    NERVOUS    SYSTEM. 


123 


much-branched  processes,  reach  to  the  surface  of  the  spinal  cord,  where  they 
terminate  in  expanded  ends  and  form  a  distinct  border  or  glia-zone.  Two 
varieties  of  the  developed  cells,  united  by  many  transitional  forms,  may  be 
distinguished:  the  "mossy-cells"  and  the  "spider-cells."  The  mossy-cells 
possess  shorter,  very  richly-branched  processes,  and  not  infrequently  are  applied 
to  the  blood-vessels  ;  they  occur  chiefly  in  the  gray  substance  ;  the  spider-cells 
have  a  small  cell-body  from  which,  besides  short,  also  many  longer,  rigid,  less- 
branched  processes  radiate  ;  these  occur  chiefly  in  the  white  substance  and  are 
not  apt  to  be  confused  with  the  ganglion-cells.  By  the  interlacing  of  the 
numerous  fine  processes  of  neighboring  glia-cells  (they  do  not  anastomose)  a 
close  web  is  constructed  which  envelops  each  individual  nerve-fiber. 

In  the  gelatinous  substance  of 
the  central  canal  and  the  posterior  white  matter.  "Giia-zone." 
cornua  the  neuroglia  assumes  a  totally 
different  appearance.  In  the  former 
the  Deiters's  cells,  with  their  (in  this 
situation)  very  long,  stiff,  undivided 
processes  are  concentrically  arranged 
in  a  fiber-wreath  (Fig.  85).  These 
and  the  cells  of  the  ependyma  aix 
also  together  called  "central  ependy 
ma  filaments."  The  substantia  gela- 
tinosa  Rolandi,  in  addition  to  the 
small  ganglion-cells  and  the  nerve- 
fibers  (collateral  fibers)  traversing  it. 
consists  of  a  granular  substance  — 
transformation  of  the  numerous  ane 
very  delicate  processes  of  Deiter>  - 
cells  occurring  here. 


f^ 


,^ 


"  ■  J 

ledullated 
erve-fibers 
onsisting  of— 

■  .\x 

is-cylinder 

and 

■-  Me 

dullary 

sheath. 

,Gli 

a-cells. 

Blood-vessels. 


Techn.  No.  69. 


THE  BRAIN.  Fig.  86.-From 

Spinal  Coku  : 

The  brain,  like  the  spinal  cord,        Column,   x  .s 
is  composed  of  a  white  and  a  gray 

matter,  which  in  their  minute  structure  agree  on  the  whole  with  the  same 
substances  in  the  cord.  But  the  arrangement  of  the  two  substances  in  the 
brain  is  a  much  more  diversified  one  than  in  the  spinal  cord. 

The  gray  substance  of  the  brain  occurs  in  four  aggregations:  i,  as  the 
cerebral  cortex,  the  outer  sheet  covering  the  surface  of  the  cerebral  hemi- 
spheres ;  2,  in  the  form  of  discrete  masses  in  the  cerebral  ganglia, — the  corpora 
striata,  the  optic  thalami,  the  corpora  quadrigemina  ;  3,  as  the  lining  of  the  ven- 
tricles, which  is  the  direct  continuation  of  the  gray  substance  of  the  spinal  cord  ; 
4,  as  the  cerebellar  cortex,  the  sheet  covering  the  surface  of  the  cerebellum. 

Discrete  masses  also  occur  in  the  interior  of  the  cerebellum.  All  these 
aggregations  have  numerous  connections  with  one  another  by  means  of  fiber- 
tracts. 


Layer  ol 

small 

pyramidal 


miiiiju^^i 


m 


Superra-       --  ^  M  '    *  "*^    ^    i  .  A 

dial  >  J   *    :  i       fcj 

rcticulu 


.Ui- 


1      Layer  ot 
\        large 
'    pyramidal 


I  I 


Interra-       y^ 

dial         -— ' 

reticulum. 


:\.'i' 


Layer  ot 
polymor- 
phous 


"iG.  88.— Scheme  of  Cerebral  Cortex,  sketched 
from  specimens  prepared  according  to  Techn.  No. 
73  b.  I.  CellofCajal.  2,  2'.  Small  pyramidal  cells. 
3.  Large  pyramidal  cell.  4.  Polymorphous  cell.  5, 
5'.  Cells  of  the  second  type.  6.  Nerve-fiber  ending  in 
the  superficial  zone  ;  a,  mossy-cell ;  i,  spider-cell. 


THE   CENTRAL    NERVOUS   SYSTEM. 


125 


The  Cerebrum. 
In  vertical  sections  of  the  cerebral  cortex  four  zones,  not  sharply  defined 
from  one  another,  may  be  distinguished  : — 

1.  The  molecular  layer  (neuroglia  layer),  the  most  superficial,  in  ordinary 
preparations  appears  finely  granular  or  reticulated,  and  contains,  besides  a  few 
cells,  an  interlacement  of  medullated  nerve-fibers  running  horizontally,  the  tan- 
gential fibers  (Fig.  87).  By  means  of  Golgi's  method,  it  may  be  seen  that  the 
reticulum  is  formed  in  part  by  the  dendrites  of  the  pyramidal  cells  (of  the  second 
and  third  zones)  and  in  part  by  the  processes  of  glia-cells.  Besides  the  latter 
there  are  in  the  molecular  zone  the  cells  of  Cajal ;  these  possess  an  irregularly- 
shaped  cell-body  and  processes  nmning  parallel  to  the  surface,  from  which 
ascending  lateral  twigs  diverge  (Fig.  88,  i).     In  the 

lower  animals  four  or  more  processes  have  been 
described  ;  in  man  these  cells  have  only  been  ob- 
served in  the  embryo,  and  evidence  of  the  nerve- 
processes  was  not  obtainable.  The  nervous  nature 
of  Cajal's  cell  is,  therefore,  not  yet  determined. 

2.  'Y\\t  zotte  of  the  small  pyramidal  cells  (Y'xg.  87 
and  88)  is  characterized  by  ganglion-cells  10  to  12  /i 
in  size  and  of  a  pyramidal  form  ;  the  apex  of  the 
pyramid  is  prolonged  into  a  long  ramifying  proto- 
plasmic process,  which  after  giving  off  minute  lateral 
twigs  enters  the  molecular  zone,  where  it  terniinates 
in  numerous,  often  serrulate,  branches  (Fig.  88,  2)  ; 
smaller  dendrites  spring  from  the  lateral  and  inferior 
surfaces  of  the  cell.  The  axis-cylinder  process  pro- 
ceeds from  the  base  and  after  giving  off  branched 
collateral  fibers  passes,  as  a  rule,  toward  the  white 
substance  to  become  the  axis-cylinder  of  one  or,  by 
division,  of  two  nerve-fibers ;  occasionally,  however, 
it  bends  and  runs  to  the  molecular  layer,  where  it 
divides  and  enters  the  web  formed  by  the  tangential  fibers  (Fig.  88,  2').  The 
nerve-processes  and  also  the  collateral  fibers  are  enveloped  in  a  medullated 
sheath.  The  size  of  these  cells  is  difficult  to  determine  because  of  the  extension 
of  the  cell-body  into  the  apical  process. 

3.  'Y\\Q  zone  of  the  large  pyramidal  cells  \i  A\i\\x\g\wi\\^A  from  the  second 
zone  by  the  greater  size  of  its  elements  (20  to  30  //)  ;  the  robust  axis- 
cylinder  process,  after  giving  off  in  the  gray  substance  several  collateral  fibrils, 
always  goes  to  the  white  substance  (Fig.  88,  3). 

4.  In  the  layer  of  the  polymorphous  nerve-cells  the  majority  of  the  elements 
are  oval  or  polygonal  ;  an  apical  dendrite  is  wanting,  but  the  delicate  nerve- 
process,  after  sending  off  a  number  of  lateral  twigs,  enters  the  white  substance, 
where  it  passes  into  one,  or,  dividing  into  T-branches,  into  two  nerve-fibers 
(Fig.  88,  4). 


Nerve-process. 

IG.89,  — PvramidalCell  fkom 
A  Fbkpendicl'lak  Section  op 

THE    CbkRDRAL    CoKTEX    OP 

Adult  Man.  X  120.  1  he 
terminal  branches  of  the  den- 
drites running  toward  the  mole- 
cular layer  aie  not  visible. 
Techn.  No.  73  b. 


126 


HISTOLOGY. 


In  the  last  three  zones  ganglion-cells  of  the  second  type  are  also  found. 
Their  branching  axis-cylinder  process  is  either  confined  to  the  gray  matter  in 
the  vicinity  of  the  cell,  or  extends  to  the  molecular  zone,  where  after  rapid 
branching  it  terminates  (Fig.  88,  5,  5'). 

The  last  two  zones  both  contain  nmiierous  meduUated  nerve-fibers  arranged 
in  part  in  thick  "radiating"  bundles,  which  split  up  into  single  fibers  near 
the  zone  of  the  small  pyramidal  cells  (Fig.  87).  The  bundles  are  formed  by 
the  descending  medullated  nerve-processes  of  the  large  and  small  pyramidal 
cells,  and  by  thick  medullated  nerve-fibers  of  unknown  source,  that  ascend 
from  the  white  substance  toward  the  cortex  (Fig.  88,  6),  where  they  divide 
repeatedly  and  form  the  "  superradial "  and  the  tangential  interlacement  (Fig. 
88),  and  finally  end  in  free  branches  ;  another  set  of  medullated  nerve-fibers 
runs  transversely  to  the  radiating  bundles  and  forms  the  interradial  reticulum. 


Blood-vessel 


Mossy-cells. 
go.^FROM  Sections  of  Br 


Spider-cell. 
X  280.     Techn.  No.  73  b. 


which  is  somewhat  condensed  toward  the  "superradial"  reticulum,  and  rep- 
resents the  stripes  of  Gennari  or  Bai/Iarger  (Fig.  87).  This  and  the  interra- 
dial reticulum  are  composed  of  the  medullated  collateral  fibrils  of  the  nerve- 
processes  of  the  pyramidal  cells. 

The  structure  of  the  cerebral  cortex  is  modified  in  certain  localities.  In 
the  hippocampal  and  uncinate  convolutions  the  tangential  fibers  are  present  in 
large  numbers  and  form  a  net-like  extended  white  layer,  the  substantia  re- 
ticularis alba.  In  the  vicinity  of  the  calcarine  fissure  the  stripes  of  Gennari 
are  developed  into  the  bundle  of  Vicq  d'Azyr,  which  may  be  seen  by  the  unaided 
eye.  Greater  or  lesser  deviations  occur  in  many  other  localities,  which  render 
a  division  of  the  above  description  much  more  difficult. 

Finally,  extensions  of  the  pia  that  penetrate  the  cerebral  cortex  in  company 
with  the  blood-vessels  participate  in  its  construction,  as  also  the  neuroglia, 
which  like  that  of  the  spinal  cord  consists  of  ependymal  cells  and  Deiters's  cells. 


ir 


THE    CENTRAL    NERVOUS    SYSTEM.  1 27 

In  the  embryo  the  peripheral  processes  of  the  former  extend  to  the  free  surface. 
Of  the  latter  two  varieties  are  distinguished,  as  in  the  spinal  cord  :  the  spider- 
cells,  which  occur  chiefly  in  the  white  substance,  and  the  mossy-cells,  which  are 
found  mainly  in  the  gray  substance,  where  they  are  in  intimate  relation  with 
the  blood-vessels,  to  the  walls  of  which  they  are  often  attached  by  one  thick 
process  (Fig.  90).  On  the  surface  of  the  cerebral  cortex  there  is  a  glia-zone 
composed  essentially  of  the  processes  of  the  glia-cells. 

The  Cerebral  Ganglia. 
The  gray  substance  of  the  cerebral  or  basal  ganglia  consists  of  ganglion- 
cells  varying  in  size,  medullated  nerve-fibers,  and  neuroglia.  Macroscopical 
variations  in  color  depend  on  the  proportions  in  which  the  ganglion-cells  and 
nerve-fibers  are  mingled  :  wealth  of  ganglion-cells  is  rendered  perceptible  by  a 
dark  red-brown  color,  profusion  of  ner\'e-fibers  by  a  pale  yellow-gray  color. 

The  Gray  Substance  of  the  Ventricles. 

The  gray  substance  extends  from  the  floor  of  the  fourth  ventricle  through 
the  aqueduct  of  Sylvius  into  the  third  ventricle,  to  the  tuber  cinereum  and  the 
infiindibulum.  It  is  of  especial  interest 
as  the  place  of  origin  of  the  cranial 
nerves.  It  is  composed  of  neuroglia, 
nerve-fibers,  and  ganglion-cells  ;  the 
majority  of  the  latter  are  multipolar, 
and  in  certain  localities  are  dis- 
tinguished by  their  size  (as  in  the 
nucleus  of  the  hypoglossal  nerve),  or 
by  their  peculiar  form  (as  the  spherical 
ganglion-cells  in  the  upper  pair  of 
the  corpora  quadrigemina). 

An  extension  of  the  neuroglia 
and  ependyma  lining  the  central  canal 
of  the  spinal  cord  lines   the  floor  of 

the  fourth  ventricle,  the  aqueduct  of  Sylvius,  the  inner  surface  of  the  third  and 
the  lateral  ventricles ;  it  is  composed  of  similar  elements.  The  columnar  or 
cubical  cells  of  the  ependyma  of  the  ventricles  in  the  newborn,  and  in  part  also 
in  the  adult,  possess  cilia. 

The  Cerebellum. 

The  cerebellum  consists  of  a  cortical  layer  of  gray  substance  composed  of 
three  well-defined  strata,  of  which  the  outer  and  the  inner  are  macroscopically, 
the  middle,  on  the  contrary,  only  microscopically  perceptible:  they  are  from 
within  outward,  the  granule  layer,  the  layer  of  the  cells  of  Piirkiiije,  and  the 
molecular  layer. 

The  granule  layer,  the  innermost,  is  characterized  by  its  rust  color  and 
consists  of  numerous  strata  of  small  cells,  which  by  the  ordinary  methods  ex- 


-  Outer 

layer 


128 


HISTOLOGY. 


hibit  a  proportionately  large  nucleus  and  a  small  amount  of  protoplasm.  By  the 
aid  of  Golgi's  method  it  becomes  apparent  that,  apart  from  the  glia-cells,  two 
kinds  of  ganglion-cells  are  present  :  small  granule-cells  and  large  granule-cells 
(Fig.  92  and  94,  i).  The  former  are  multipolar  ganglion-cells  with  short  proto- 
plasmic processes,  with  claw-like  endings,  and  a  delicate  nerve-process,  with- 
out a  medullary  sheath,  which  passes  vertically  into  the  outermost  or  molecular 
layer  ;  there  it  divides  into  longitudinal  T-branches  running  parallel  to  the  sur- 
face and  terminating  in  free  unbranched  ends.     The  small  granule-cells  are  the 


Fig.  93.— Large  Granule-cell  from  a  Section  Through  the  Cortex 
OF  THE  Cerebellum  of  a  Six-Webks'-Old  Cat.      X  "oo.     Techn. 

No.  74. 


through  the  cortex  of  the  cere- 
bellum of  .1  six-weeks'-old  cat. 
X  400.     Techn.  No.  74. 


principal  elements  of  the  granule-layer.  Less  numerous  are  the  large  granule- 
cells,  multipolar  ganglion-cells  more  than  twice  the  size  of  the  smaller  elements, 
whose  ramifying  protoplasmic  processes  extend  into  the  outermost  layer,  and 
whose  nerve-process,  running  in  the  opposite  direction,  rapidly  divides  and 
terminates  in  a  rich  ramification  penetrating  within  the  granule-layer  (Fig.  93 
and  94,  2). 

A  dense  plexus  of  medullated  nerve-fibers  occurs  in  the  granule-layer  ;  the 
greater  part  of  the  fibers  come  from  the  white  substance  of  the  cerebellum,  and 


THE    CENTRAL    NERVOUS    SYSTEM. 


129 


at  the  boundary  of  the  granule  and  middle  layers  they  form  a  horizontal  band, 
transverse  to  the  longitudinal  axis  of  the  convolution,  from  which  fibers  run 
into  the  molecular  layer.  A  small  portion  of  this  plexus  is  formed  by  the 
medullated  nerve-processes  of  the  cells  of  Purkinje  (Fig.  94,  3,  3',  3"). 

The  middle  stratum  of  the  cerebellar  cortex  consists  of  a  simple  layer  of 
very  large  multipolar  ganglion-cells,  the  cells  of  Purkinje.  Their  somewhat 
pear-shaped  bodies  send  two  robust  protoplasmic  processes  into  the  molecular 
layer,  where  they  terminate  in  an  imcommonly  rich  arborization  extending  to 


Molecular  l.iyi 


Granulclaycr. 


Fig.  94.— Sciibmb  of  the  Ci 
74.     1.  Small  grantilc-celli 

V',  fibers  of  the  molecular  layer.    4.  l_ell  01  rurlcinie. 
Glia-cells  ;    a,  of  the  molecular  layer ;  ^,  mossy-cell;  f,  spldei 


BBBLLAR  CoRTEX,  skctchccl  from  a  specimen  prepared  according  to  Techn.  No. 
».   Large  granule-cells.     3.  Network  of  nerve  fibers ;    3',  horizontal  bundles: 
Cell  of  Purkinje.     5.  BaskeKell.     6.  Small  cortical  cells. 


the  free  surface  (Fig.  94,  4).  The  ramification  does  not  extend  in  all  direc- 
tion, but  only  in  planes  transverse  to  the  long  axis  of  the  convolution.  The 
entire  ramification  can,  therefore,  only  be  seen  in  sections  at  right  angles  to  the 
long  axis  of  the  convolution.  From  the  opposite  pole  of  the  cell  the  axis- 
cylinder  process  proceeds,  which  soon  acquires  a  medullated  sheath  and,  pass- 
ing through  the  granule-layer,  enters  the  white  substance  of  the  cerebellum  ; 
while  still  within  the  granule-layer  it  sends  off  collateral  fibrils,  which  branch 
and,  in  part,  run  hack  between  the  cells  of  Purkinje  (Fig.  94). 
9 


13° 


HISTOLOGY. 


The  molecular-layer  is  distinguished  by  its  gray  color  and  contains  two 
kinds  of  multipolar  ganglion-cells  :  the  lai-ge  cortical  cells  or  basket-cells  and 
the  small  cortical  cells.  The  large  cortical  cells  lie  in  the  deeper  half  of  the 
molecular-layer ;  their  protoplasmic  processes  extend  mainly  toward  the  surface. 
Their  longer  nerve-process  runs  horizontally  near  the  inner  margin  of  the 
molecular-layer,  transversely  to  the  axis  of  the  convolution,  sends  toward  the 
surface  a  few  collateral  fibrils,  and  in  the  deeper  portions  of  the  layer  gives  off 
at  successive  intervals  delicate  branches  whose  terminal  ramifications  form  a 
basket-like  network — fiber-basket — around  the  bodies  of  Purkinje's  cells  (Fig. 
95).  The  "basket"  often  also  embraces  the  beginning  of  the  axis-cylinder 
process  of  Purkinje's  cell.  Nearer  to  the  surface  lie  the  small  cortical  cells 
(Fig.  96)  ;  their  nerve-process  is  difficult  to  find,  and  consequently  has  been 
but  little  investigated. 


Fig.  95. — Baskbt-Cbll,  from  a  Section  ■ 

X  240.     The  five  cells  of  Purkinje  were  not  blackened,  but  plainly  ■ 
are  sketched.     Techn.  No.  74. 


The  medullated  nerve-fibers  in  the  molecular-layer  are  extensions  of  the 
reticulum  of  the  granule-layer,  and  pass  in  part  to  the  surface,  where  after  los- 
ing the  medullary  sheath  they  terminate  in  free  branches  between  the  arboriza- 
tion of  the  protoplasmic  processes  of  the  cells  of  Purkinje,  and  in  part  they 
run  horizontally  between  the  bodies  of  these  cells,  parallel  to  the  axis  of  the 
convolution. 

The  neuroglia  of  the  cerebellum  consists  of  two  kinds  of  cells :  the  one 
kind  lie  at  the  boundary  of  the  granule-layer,  and  have  small  bodies  which 
send  a  few  short  processes  inward,  but  many  long  processes  in  a  straight  course 
toward  the  free  surface,  where  they  terminate  in  a  triangular  expansion  (Fig. 
97,  left),  and  form  in  this  way  a  relatively  thick  peripheral  glia-layer  ;  the  other 
kind,  stellate  cells,  resemble  the  mossy-cells  of  the  cerebral  cortex  (Fig.  97, 
right)  ;  they  occur  in  all  the  strata.  In  the  white  substance  typical  spider-cells 
are  found. 


THE    CENTRAL    NERVOUS    SVSTEM. 


131 


So  long  as  the  cerebellum  is  not  fully  developed  it  is  characterized  by  a 
series  of  peculiarities  which  are  wanting  in  the  adult.  In  embryos  and  young 
animals  there  is  over  the  as  yet  slightly-developed  molecular-layer  a  superficial 
granule  stratum  ;  the  structures  in  the  granule-layer  described  under  the  name 
of  "  moss-fibers  "  are  developmental  forms  of  meduUated  nerve-fibers  ;  and  of 
like  significance  are  the  "climbing  plexuses"  found  in  the  environs  of  the 
ramifying  protoplasmic  processes  of  the  cells  of  Purkinje. 

The  union  of  the  elements  of  the  cerebellum — as  everywhere  in  the  central 
nervous  system — is  by  contact,  not  by  direct  connection. 


Small  cortical  cells. 


Cell  of  Purkinje.  .. 


Ascending  i 


Fig.  96. — Fkom  a  Srction  of  thb  Cbrsbgllar  Cortex  op  Adult  Man.  X  240. 
nerve-processes  of  bitsket-cells.  The  cell  at  Purkinje  and  the  glia-cell  are  drawr 
specimen  for  the  purpose  of  demonstrating  the  difference  in  size.     Techn.  No.  74. 

The  white  substance — the  medulla — of  the  cerebrum  and  of  the  cerebel- 
lum, apart  from  the  elements  of  the  supporting  framework  (connective  tissue 
and  neuroglia),  consists  throughout  of  medullated  nerve-fibers  without  a  neuri- 
lemma and  varying  in  thickness  from  2.5  to  7/1. 

The  hypophysis  cerebri  (pituitary  body)  is  composed  of  two  genetically 
different  jiarts  :  (i)  a.  sma/l posterior /obe  i\\3X  belongs  to  the  brain,  its  stalk 
the  infundibulum  ;  it  however  contains  but  few  nerve-fibers,  and  consists  prin- 
cii)ally  of  connective  tissue,  blood-vessels,  and  cells  which  closely  resemble 
bipolar  or  multipolar  ganglion-cells;   (2)  an  anterior  larger  lobe  derived  as  a 


132 


HISTOLOGY. 


diverticulum  from  the  primary  oral  cavity  ;  it  contains  tubular  acini  embedded 
in  loose  vascular  connective  tissue,  the  majority  of  which  are  solid  and   filled 
with  pale  or  dark  cubical  epithelial  cells  (Fig.  98).     Only  a  few  of  the  acini 
at  the  edge  of  the  smaller  lobe  are  hollow  ;  occasion- 
ally they  contain  colloid  substance  resembling  that 
in  the  tubules  of  the  thyroid  body. 

The piiicaU'ody  (epiphysis, conarium,)  isderived 
from  a  diverticulum  of  the  primitive  brain-vesicle 
and  consists  of  epithelial  cells,  some  of  which  have 
delicate  processes,  and  of  a  connective-tissue  envelope 
from  which  septa  extend  into  the  interior  of  the 
body,  in  which  almost  invariably  the  so-called 
"brain-sand"  is  found,  rounded  concretions  vary- 
ing in  size  and  having  uneven,  mulberry-like  sur- 
faces (Fig.  99).  They  are  composed  of  an  organic 
basis  and  calcium  phosphate  with  magnesium  phos- 
phate. 

Not  infretpiently  (especially  in   advanced  life) 
there  occur  in  the  brain  substance  round  or  discoid 
bodies  exhibiting  distinct  concentric  striation,  stain- 
ing violet  on   treatment  with  iodine  and  sulphuric 
acid,  and  therefore  related  to  amylum  (Fig.  100,  «).     These  corpora  amylacea 
are  almost  constant  within  the  walls  of  the  ventricles  of  the  brain,  and  are  also 
present  in  many  other  localities,  as  well  in  the  gray  as  in  the  white  substance. 


IN.  X  90.  On  the 
right  the  body,  P,  and  the 
dendrites,  P' ,  of  a  cell  of  Pur- 
kinje  are  sketched  to  demon- 
strate the  difference  between 
this  element  and  the  glia-cells. 
Techn.  No.  74. 


Blood-vessel 
taining  bit 
corpuscles. 


*-.»f      'tt.^.sr—  ** Colloid  "  sub- 


FiG.  08 
Tech 


Portion  of  Horizontal  Shction  of  Human  Pituitary  Body,  showing  the  boundary  line  betw 
iterior  and  posterior  lobe.  Two  gland-tubules  on  lire  left  contain  each  a  dark  epithelial  cell.  X 
n.  No.  75. 


The  Me.mbr.^nes  of  the  Central  Nervous  SvsTE^L 
Two  connective-tissue  membranes  envelop  the  brain  and  the  spinal  cord  : 
the  dura  and  the//t;. 


THE    CENTRAL    NERVOUS    SYSTEM.  I33 

The  dura  of  the  spinal  cord  consists  of  compact  connective  tissue  and 
numerous  elastic  fibers,  flat  connective-tissue  cells  and  plasma-cells  (Fig.  103). 
The  inner  surface  is  covered  by  a  simple  layer  of  flat  epithelial  cells  (endothe- 
lium).    The  nerves  and  the  blood-vessels  are  not  numerous. 

The  dura  of  the  brain  forms  also  the  periosteum  of  the  inner  surface  of 
the  cranium  and  consists  of  two  lamellae  ;  an  inner,  corresponding  to  the  dura 
of  the  cord,  and  of  like  structure,  and  an  outer,  corresponding  to  the  periosteum 
of  the  vertebral  canal.  It  is  composed  of  the  same  elements  as  the  inner 
lamella,  with  the  exception  that  the  outer  fiber-bundles  are  disposed  trans- 
versely to  the  inner.  The  outer  lamella  is  rich  in  blood-vessels,  which  pass 
from  it  into  the  cranial  bones. 

The  pia  of  the  brain  and  spinal  cord  is  a  two-layered  sack.  The  outer 
layer,  the  arachnoid  of  authors,  is  covered  on  its  free  surface  by  a  simple  layer 
of  epithelium  (endothelium),  and  is  not  closely  attached  to  the  dura.  The 
inner  layer   (pia)  closely  invests  the  surface  of  the  brain  and  cord,  and  sends 


Fig.  99. — AcBRvuLus  C 
Body  op  a  Woma 
Techn.  No.  76. 


^WiW 


\i  f 


^IG.  100. — From  a  Tbased  Preparation  of  Gray 

SUBSTAN'CB   FROM    THE   WaLL  OF   A    VbNTRICLB   OF 

Human  Brain.     X  240.    a.  Corpora  amylacca  ;  b, 
myelin  drops ;  c,  red  blood-corpuscles  ;  d,  epcndy- 


mal  cells :  ^,  meduUated 
ell.    Techn.  No.  77. 


:-fibers ;  _/",  ganglic 


into  their  substance  processes  carrying  blood-vessels.  The  arachnoid  and  the 
pia  are  joined  together  by  numerous  trabeculae  extending  from  the  inner  surface 
of  the  former  to  the  outer  surface  of  the  latter.  Hernia-like  evaginations  occur 
on  the  outer  surface  of  the  arachnoid  in  certain  localities,  in  particular  near 
the  superior  longitudinal  sinus,  and  push  the  attenuated  dura  before  them  into 
the  venous  sinus.  These  are  the  so-called  villi  of  the  arachnoid,  which  under 
the  name  Pacchionian  bodies  were  long  regarded  as  pathologic.  The  pia  is 
composed  of  delicate  connective-tissue  bundles  and  plate-like  cells  which  cover 
the  inner  surface  of  the  arachnoid  and  the  trabeculre. 

The  telm  cltoroidca  and  plexus  choroidece  are  highly  vascular  villous  pro- 
cesses on  the  margin  of  a  fold  of  the  pia  that  hang  like  a  fringe  within  the  ven- 
tricles ;  they  consist  of  connective  tissue  and  blood-vessels,  whose  fine  ramifi- 
cations are  united  into  tufts  or  lobules.  They  are  covered  by  a  simple  layer  of 
cubical  epithelial  cells,  ciliated  in  the  newborn,  which  enclose  pigment -granules 
or  oil-elobules. 


134  histology. 

The  Vessels'  of  the  Central  Nervous  System. 

The  blood-vessels  of  the  central  nervous  system  form  a  narrow-meshed 
capillary  network  in  the  gray,  a  wide-meshed  network  in  the  white  substance. 
The  blood-vessels  possess  a  so-called  adventitial  sheath  (perivascular  lymph- 
sheaths)  often  consisting  of  only  a  simple  stratum  of  endothelial  cells.  The 
walls  of  the  intradural  venous  sinuses  are  composed  of  a  simple  endothelial 
membrane. 

The  Lymph  Channels. — Between  the  dura  and  the  arachnoid  there  is  a 
capillary  cleft  or  fissure,  the  subdural  space,  which  communicates  with  the  deep 
cervical  lymph- vessels  and  lymph-nodes  (at  least  in  the  rabbit  and  the  dog), 
with  the  lymph  channels  of  the  peripheral  nerves,  with  the  lymph-vessels  of  the 
nasal  mucous  membrane,  with  the  smaller  clefts  (juice-canals)  in  the  dura, 
and  finally,  round  the  arachnoidal  villi,  with  the  intradural  venous  sinuses. 
The  fluid  in  the  subdural  space  is  very  scanty. 

The  subarachnoidal  space,  that  between  the  two  layers  of  the  pia — (arach- 
noid and  pia) — communicates  with  the  "juice  channels"  of  the  peripheral 
nerves,  the  lymph-vessels  of  the  nasal  mucous  membrane,  the  interior  of  the 
ventricles  of  the  brain  and  of  the  central  canal  of  the  spinal  cord.  The  fluid 
in  the  subarachnoid  space  is  very  abundant ;  it  is  called  the  cerebrospinal 
fluid. 

The  perivascular  lymph-spaces  are  also  in  communication  with  the  subarach- 
noid spaces,  and  may  be  injected  from  the  latter. 

The  spaces  filled  only  by  injecting  the  brain  substance  itself  cannot  be 
included  in  the  system  of  lymphatic  channels.  These  spaces  occur  as  pericel- 
lular spaces  surrounding  the  larger  ganglion-cells  of  the  cerebral  cortex,  also 
many  glia-cells  ;  as  perivascular  spaces  of  the  blood-vessels,  that  formed  by  the 
adventitial  sheath  excepted ;  and  between  the  pia  and  the  cerebrum,  as  the 
epicerebral  space.      These  may  be  regarded  as  a  separate  juice-canal  system. 


2.  THE  PERIPHERAL  NERVOUS  SYSTEM. 

The  Nerve-Trunks. 
The  cerebro-spinal  neme-trunks  are  composed  chiefly  of  medullated  nerve- 
fibers  varying  in  thickness  and  only  a  few  gray  nerve-fibers,  and  therefore  by 
reflected  light  appear  white.  Their  mode  of  union  agrees  in  many  respects 
with  that  of  the  striated  muscle-fibers.  A  sheath  formed  of  loose  connective 
tissue  and  elastic  fibers,  often  containing  clusters  of  fat-cells,  surrounds  the 
entire  nerve-trunk.  It  is  called  the  f//>/f//r////«  (Fig.  loi).  E.xtensions  of  the 
epineurium  into  the  interior  of  the  nerve  surround  the  so-called  secondary 
nerve-fiber  bundles  (funiculi),  each  of  which  is  enveloped  by  the  concentri- 
cally lamellated  connective-tissue  perineurium.  From  the  latter  connective- 
tissue  septa  extend  into  the  interior  of  the  secondary  nerve-fiber  bundles  ;  they 


THE    PERIPHERAL    NERVOUS    SYSTEM. 


135 


constitute  the  eiidoneurium.  Finally,  delicate  offsets  from  the  endoneurium, 
the  fibrillar  septa,  corresponding  to  the  endomysium  of  the  single  muscle-fiber, 
surround  each  individual  nerve-fiber.  These  sheaths  are  in  direct  connection 
with  the  tissue  of  the  dura  and  the  pia.  Perineurium  and  endoneurium  are 
composed  of  bundles  of  fibro-elastic  tissue  arranged  in  a  number  of  lamellae 


Artery. 


Epineurium. 


-Portion  of  Ckoss-S 


Human  Median  Nbrve.     X  20.     Techn.  No.  79. 


concentrically  disposed  ;  each  lamella  is  lined  by  a  simple  layer  of  flattened 
connective-tissue  cells,  whose  outlines  can  be  demonstrated  by  silver  staining. 
The  fibrillar  septa  also  consist  of  delicate  connective-tissue  bundles  lined  by 
endothelioid  plates. 


Fibrillar  sheath. 


The  nerve-fiber  bundle  not  infrequently  divides;  a  variable  number  of 
nerve-fibers  branch  off  from  one  funiculus  to  join  another,  and  the  result  is  a 
plexus  of  nerve-fiber  bundles.  Division  of  the  nerve-fibers  does  not  occur  until 
at  the  periphery. 

The  sympathetic  iiervc-tninks  are  in  part  white  and  in  part  gray  in  color, 
depending  upon  the  greater  or  lesser  number  of  meduUated  nerve-fibers  present : 


136  HISTOLOGY. 

for  example,  the  splanchnic  nerves  contain  many  medullated  nerve-fibers,  while 
the  gray  branches  of  the  abdominal  and  pelvic  plexuses  contain  only  a  few  of 
the  thinnest  medullated  and,  on  the  other  hand,  numerous  nonmeduUated 
nerve-fibers.  The  nerve-fibers  are  held  together  and  grouped  into  bundles  by 
connective  tissue. 

The  blood-vessels  run  lengthwise  within  the  epineurium,  and  form  within 
the  perineurium  and  endoneurium  capillary  networks  with  elongated  meshes. 

The  lymph  channels  are  represented  by  the  spaces  between  the  lamellae  of 
the  perineurium  and  between  the  individual  nerve-fibers  ;  these  are  in  commu- 
nication with  the  sub-dural  and  the  sub-arachnoidal  spaces,  but  not  with  the 
lymph- vessels  accompanying  the  nerve-trunk. 


Nucleated  sheath 


Is^^^ 


i.  103. 

—  Pi 

11  he 

°ee, 

OF  CROi 

1  in  such 

;s-Shct1( 

aprocess. 

In 

the  axis 

of  the  t 

HE  Gassbrian  Ganglion  of  Man.  X  240.  The  cell-processes 
At  X  the  protoplasm  of  the  ganglion-cell  has  retracted  and  simulates 
ly  cut  nerve-fibers  the  axis-cylinders  are  seen  in  section.     Techn. 


The   Gangli.\. 

Ganglia  are  groups  of  nerve-cells  occurring  along  the  course  of  the  nerve- 
trunks.  They  are  usually  macroscopic  in  size,  and  contain  small  bundles  of 
nerve-fibers  between  which  lie  ganglion-cells  arranged  in  rounded  groups  or  in 
longitudinal  rows.  A  connective-tissue  capsule,  an  extension  of  the  epineurium, 
covers  the  outer  surface  of  the  ganglion  and  sends  into  the  interior  delicate 
processes  for  the  support  of  the  nerve-fibers  and  ganglion-cells.  The  blood- 
vessels are  very  numerous  and  form  a  capillary  network  which  surrounds  the 
individual  cells. 

The  cells  of  the  spinal  ganglia  are  bipolar  in  the  embryo  ;  the  processes 
spring  from  opposite  poles  of  the  cell.  In  the  course  of  development  the 
two  processes  gradually  approach  until  finally  they  proceed  from  a  com- 
mon stalk ;    the  cell    thus  becomes    unipolar.       (In    amphibians    and    birds 


THE    PERIPHERAL    NERVOUS    SYSTEM. 


137 


isolated  multipolar  ganglion-cells  occur;  their  dendrites  are,  however,  short 
and  only  slightly  branched. )  The  process  of  the  adult  cell  receives  a  medullary 
sheath  and  a  neurilemma  very  near  its  exit,  and  after  a  short  course  divides  at 
a  node  of  Ranvier  into  twoT"  or  Y-branches.  One  branch — the  cellulipetal — 
passes  as  the  axis-cylinder  of  a  sensory  nerve-fiber  to  the  periphery  of  the  body, 
the  other — the  cellulifugal — usually  the  thinner,  enters  the  spinal  cord  as  a 
constituent  of  a  posterior  nerve-root,  and  terminates  in  free  branches  in  the 
gray  substance.  Thus  each  spinal  ganglion-cell,  by  its  undivided  process,  is  in 
a  manner  intercalated  in  the  course  of  a  sensory  nerve-fiber.  The  cells  of  the 
spinal  ganglia  are  large,  round,  often  pigmented,  and  their  vesicular  nucleus 
contains  a  conspicuous  nucleolus.  Each  ganglion-cell  is  enveloped  in  a 
nucleated  cajisule  consisting  of  concentric  strata  of  flat  connective-tissue  cells, 
which  is  prolonged  on  to  the  process  of  the  cell  as  l\iz  fiber- sheath  (neurilemma). 
Whether  any  nerve-fibers  pass  through  the  spinal  ganglia  that  do  not  enter 
into  relation  with  the  ganglion-cells  is  uncertain.  In  young  embryo  chicks 
such  fibers  have  been  seen  coming  from  the  cells  of  the  anterior  cornua,  but 
they  have  not  been  found  in  mammals. 


Artcrj'  in  transvei 


Nuclcaled  sheath 


Fig.  104. — Portion 


Nucleated  sheath  (from 
the  surface). 


X  240.     Techn.  No.  81 


Gray  nerve-fibers  from  the  sympathetic  occur  in  the  spinal  ganglia ;  they 
branch  and  form  a  plexus  in  the  connective-tissue  capsule  of  the  ganglion-cells. 

Other  ganglia  possessing  the  same  structure  as  the  spinal  ganglia  are :  the 
Gasserian,  the  jugular,  the  plexus  nodosus  of  the  vagus,  the  petrosal,  and  the 
geniculate ;  the  ganglion  of  the  auditory  nerve  (ganglia  nervi  cochlepe  et  nervi 
vestibuli)  contains  bipolar  cells. 

The  sympathetic  ganglia  consist  of  nerve-fibers  and  small,  often  pigmented, 
cells  surrounded  by  a  nucleated  capsule  and  possessing  one  or  two  nuclei  (two 
in  the  rabbit  and  the  guinea-pig).  The  cells  are  multipolar  ;  the  axis-cylinder 
process  passes  directly  into  a  nerve-fiber ;  the  varicose  ramifications  of  the  pro- 
toplasmic processes  surround  the  neighboring  ganglion-cells.  The  nerve-fibers 
are  partly  thin  medullated,  partly  nonmedullated  fibers;  their  terminal  ramifi- 
cations in  part  surround  the  ganglion -cells.  The  nerve-cells  of  the  symjia- 
thetic  ganglia  of  fishes  are  bipolar.  In  amphibians  ganglion-cells  occur  in 
which  the  single  process  with  T-branches  is  surrounded  by  a  spiral  fiber. 


138 


HISTOLOGY. 


THE  PERIPHERAL  NERVE-ENDINGS. 

Terminations  of  Sensory   Nerves. 

The  peripheral  terminal  branches  of  the  sensory  nerves  are  distributed 
naked,  as  free  endings,  or  they  are  enclosed  by  epithelial  or  connective-tissue 
cells  and  terminate  as  special  endings  (terminal  corpuscles,  end-organs). 

Free  endings  are  formed  as  follows  :  a  medullated  nerve-fiber  in  passing 
to  its  ultimate  distribution  loses  its  medullated  sheath,  divides  repeatedly,  and 
forms  a  plexus  of  primitive  fibrils  which  terminate  in  pointed  or  club-shaped 
ends.     These  endings  occur  more  particularly  in  stratified  epithelium.      They 


Epideri 


THROUGH    T 

Yba'rs  of  Age.     X  200.     The  cell-nuclei  of  the  stratuci 

Cells    ot   LangcrhansT  n.  intr.iepilhelial  nerve-fibtrs.     /■,/>!. 

capillary  loop,  c,  of  which  only  one  limb  is  visil  ' 

ing  meduUaled  nerve-fibers.    Both  papilUc  contain  nonmedullated  r 


distinct  only  in  the  deepest  layer.  /. 
1  papillae  of  the  corium  ;  P,  contains  a 
tactile  corpuscle,  /,  with  two  approach- 
:rve-fibers.    Techn.  No.  82. 


have  been  demonstrated  in  the  cornea,  in  the  oral  mucous  membrane,  and  in 
the  deeper  strata  of  the  epidermis.  In  the  latter  cells  with  long  branched  pro- 
cesses— the  cells  of  Langcrhans — occur;  these  were  formerly  regarded  as 
migrated  wandering  cells  from  the  corium,  and  it  is  possible  that  some  of  them 
may  have  such  an  origin  ;  the  majority,  however,  are  transformed  epithelial 
cells;  all  the  transitional  forms  from  the  typical  epithelial  cells  to  the  stellate 
bodies  in  question  may  be  found. 

Sensory  nerves  have  also  been  found  in  the  muscles.  The  nerve-fibers  lose 
their  medullated  sheath  and,  invested  only  by  the  nerve-nuclei,  divide  dicho- 
tomously  ;  the  delicate  naked  fibrillae  extend  lengthwise  between  the  muscle- 
fibers  and  terminate  in  free  endings. 


THE    PERIPHERAL    NERVOUS    SYSTEM. 


139 


The  terminal  corpuscles  ox  special  endings  may  be  divided  into  two  groups  : 
tactile-cells  and  end-bulbs.  In  the  tactile-cells  the  nerve-fiber  terminates  in 
relation  with  one  or  two  cells;  in  end-bulbs  it  terminates  in  the  interior  of  a 
finely  granular  body,  the  so-called  inner  bulb. 


Tactile-cell     , 


Nerve-fiber 
Connective-tissue  sheath 


Fig.  106.— From  a  Pbrpendici;lar  Section  through  the  Skin  of  the  Great  Toe  of 
FIVE  Vbaks  Old.  X  240.  The  outlines  of  the  cells  and  nuclei  of  the  epidermis  can  onl3M>e 
X.  Tactile-ceiU  in  tile  corium,  resting  upon  the  ramifications  of  a  delicate  nerv( 


Man  Twbntv- 
:en  indistinctly. 
Techn.  No.  82. 


Tacth.e-Cells. 

These  may  be  either  simple  or  compound.  The  simple  tactile-cells  are  oval 
nucleated  bodies  measuring  6  to  12  m  (Fig.  106);  they  occur  in  the  deeper 
strata  of  the  epidermis  or  adjacent  portion  of  the  corium,  and  are  embraced 
by  the  tactile  meniscus,  a  crescentic  expansion  in  relation  with  a  nonmedullated 
nerve-fiber. 

'\:\\e  compound  tactile-cells  H^randry'i  and  Merkel's)  consist  of  two  or 
more  somewhat  flattened  cells,  each  larger  than  a  simple  tactile-cell  (15  At  deep 


:-fiber 
:re,  in  profile, 
B.  Two  com- 
ic corpuscle  " 
section. 


Fig.  107.— FnfjM  Perpendicular  Sections  Throl'Ch  the  Skin  of   the  Beak  of  a  Goose.     ^   240.     A 
Compound  tactile-cell  (simple  tactile  corpuscle),  cut  parallel  to  the  course  of  the  entering  ne         -^"^      - 
medullated  nerve-fiber  only  partially  met  by  the  section;  a,  axis-cylinder;    its  division  is  h< 
invisible;  /f,  tactile  disks  cut  perpendicularly  ;  h,  connective-tissue  sheath  ;  /s,  tactile-cells, 
pound  tactile-cells  cut  transversely  to  the  plane  of  the  entering  nerve-fiber  ;     I.  "Simple  tact 
consisting  of  four  tactile  cells  ;  2,  twin  tactile-cells  ;  ts,  tactile  disks  ;  a,  axis-cylinders  in  trans 
before  divitling;  if,  medullated  nerve  fibers;  c,  corium.     Techn.  No.  83. 

by  50  II  wide)  and  containing  a  vesicular  nucleus.  Between  the  cells  is  a  flat- 
tened tactile  disk,  which  is  embraced  between  the  forks  of  the  divided  axis- 
cylinder  of  a  medullated  nerve-fiber.  The  medullary  sheath  terminates  at  the 
point  where  the  fiber  enters  the  corpuscle  and  the  neurilemma  becomes  fused 
with  the  connective  tissue  of  the  capsule  surrounding  the  tactile-ceUs  (Fig. 
107).      The  compound  forms  containing  three  or  four  tactile-cells  have  been 


I40  HISTOLOGY. 

designated  "simple  tactile  corpuscles."  The  compound  tactile  corpuscles  have 
only  been  found  in  the  epidermis  of  the  beak  and  in  the  tongue  of  birds,  espe- 
cially in  web-footed  birds;  they  are  situated  almost  exclusively  in  the  upper- 
most strata  of  the  corium. 

End-Bulbs. 

The  end-bulbs  are  spheroidal  or  oval  bodies  in  the  interior  of  which  a 
nerve-fiber  terminates  in  a  simple  or  branched  ending.  There  are  various 
forms  of  end-bulbs. 

The  so-called  cylindrical  end-bulbs,  the  simplest  form,  consist  chiefly  of  a 
modified  extension  of  the  entering  nerve-fiber  and  comprise  three  parts, 
the  axis-cylinder,  the  inner  bulb,  and  the  capsule.  The  capsule  is  a  continua- 
tion of  the  connective-tissue  sheath  of  the  nerve-fiber.     The  inner  bulb  is  a 


is-cylinde 
er  bulb. 


r^' 


Fig.  108. — Cylindrical  End-Bulb  from  th: 
JUNCTIVA  OF  Calf.     X  240.     Tcchn.  No. 


.  Corpuscle  of  Vater  from  thb 
Cat.  >C  50.  The  cells  lining  the 
capsules  may  be  recognized  by  their  prominent  nuclei. 
The  medulla  of  the  nerve-fiber  may  be  traced  to  the 
inner  bidb.     Techn.  No.  85. 


finely  granular  mass  exhibiting  concentric  striations  and  a  few  nuclei  at  the 
periphery.  The  nerve-fiber  loses  its  medullary  sheath  before  entering  the  inner 
bulb,  into  which  the  axis-cylinder  ascends  as  a  flat  band  and  terminates  at  the 
upper  pole  in  a  free  or  club-shaped  ending.  The  cylindrical  end-bulbs  are 
found  in  the  tunica  propria  of  mucous  membranes ;  for  e.xample,  in  the  scleral 
conjunctiva  and  the  oral  mucous  membrane. 

The  corpuscles  of  ^  Vater,  or  Pacinian  bodies,  are  transparent,  elliptical 
forms,  2  to  3  ram.  long  and  i  to  2  mm.  thick,  and  like  the  cylindrical  end- 
bulbs  consist  of  a  capsule,  an  inner  bulb,  and  an  axis-cylinder;  the  two  latter 
possess  the  same  structure  as  in  the  end-bulbs,  but  the  capsule  is  differently 
formed.  It  consists  of  twenty-five  to  fifty  concentric  lamellje,  each  lined  by  a 
simple  layer  of  endothelioid  cells  and  separated  from  neighboring  lamelloe  by  a 
serous  fluid.    Each  lamella  consists  of  an  outer  transverse  and  an  inner  loneitudi- 


THE    PERIPHERAL    NERVOUS    SYSTEM.  I4I 

nal  layer  of  connective- tissue  fibers.  They  are  thinner  and  closer  together  near 
the  inner  bulb.  Along  the  course  by  which  the  entering  nerve  passes  to  the 
inner  bulb  the  lamellae  are  not  infrequently  united  by  a  longitudinal  strand  of 
tissue,  the  iiiterlamellar  ligament.  A  small  artery  accompanies  the  nerve-fiber 
into  the  interior  of  the  corpuscle  and  breaks  up  into  a  capillary  network 
between  the  concentric  lamella;. 

The  Pacinian  bodies  or  corpuscles  of  Vater  are  found  in  the  subcutaneous 
connective  tissue  of  the  palm  of  the  hand  and  the  sole  of  the  foot,  on  the  pudic 
nerves  of  the  penis  and  the  clitoris,  in  the  vicinity  of  joints,  in  the  neighbor- 
hood of  the  pancreas,  in  the  mesentery,  and  elsewhere. 

Not  infre(iuently  the  axis-cylinder  terminates  in  a  forked  ending  or  in  a 
number  of  twisted  and  interlacing  branches. 

The   corpuscles   of    Herbst    and    Key-Retzius,  <S^^ 

occurring  in  birds,  closely  resemble  the  corpuscles  "'^X 

of  Vater  ;  they  differ  only  in  being  much  smaller  and  "'        T  -  i" 

in  possessing  a  double  row  of  longitudinally-disposed  '     ^vS 

nuclei  in  the  inner  bulb.  \^     * 

The  genital  corpuscles  of  the  lower  mammals 
and  of  man  are  spherical  or  oval  forms  (0.06  mm. 
wide  by  0.4  mm.  long),  and  consist  of  a  finely 
granular  nonnucleated  inner  bulb  enveloped  in  a 
connective-tissue  capsule  containing  cells  rich  in 
protoplasm.      The   approaching    medullated    nerve-      Fig.  ho— Tactile  Corpuscle 

'  '  '  "  FKOM  A  Perpendicular  Sec- 

fibers  make  several  turns  around  the  corpuscle,  lose  tion  of  the  orbat  Toe  of 
their  medulla,  and  divide  ;   the  naked  axis-cylinders        Old.   x  560.   «.  Mcduiiaicd 

.  .  iicrvc-fibers  ;  ^,  v.iricosilics  ;  *, 

i)enetrate  the  inner  bulb  at  different  points,  undergo        connective.tissue sheath.   The 

......  ,     ^  ,  ,  r     r,      .,  nuclei  are  not  visible.     Techn. 

rapid  division,  and   form   a  dense   plexus  of   fibrils        No.  82. 
with  varicose  enlargements.     In  imperfect  staining 

the  varicosities  simulate  club-shaped  endings.  Each  plexus  is  joined  to  neigh- 
boring plexuses  by  delicate  nervous  filaments. 

The  genital  corpuscles  lie  in  the  depths  of  the  corium  at  various  distances 
from  the  i)a])illary  stratum  ;  in  the  papillae  only  smaller  corpuscles,  resembling 
the  "  simple  spherical  end-bulbs,"  are  found.  The  largest  number,  one  to  four 
to  the  square  mm.,  occurs  in  the  glans  penis  and  the  clitoris.  The  so-called 
simple  spherical  end-bulbs  (they  are  sometimes  oval)  have  a  similar  structure  ; 
they  are  found  in  the  conjunctiva  and  the  adjoining  portions  of  the  cornea,  and 
possess  a  greatest  diameter  of  0.02  to  o.  i  mm.  The  articular  corpuscles  belong 
to  the  same  category. 

The  tactile  corpuscles  (Wagner's  and  Meissner's)  are  elliptical  structures, 
40  to  100  /t  long  and  30  to  60  /i  broad,  characterized  by  cross  markings.  They 
possess  a  connective-tissue  capsule  with  flattened  cells,  the  boundaries  of  which 
and  their  transversely  placed  nuclei  produce  the  striations.  Two  or  more  medul- 
lated nerve-fibers  enter  each  corpuscle  ;  after  a  number  of  winding  excursions 
about  the  inferior  pole  of  the  corpuscle,  their  connective-tissue  sheath  blends 
with  the  tissue  of  the  capsule,  they  lose  their  medullary  sheath,  and  enter  as 


142 


HISTOLOGY. 


naked  axis-cylinders  into  a  granular  substance  corresponding  to  an  inner  bulb; 
there  they  form  a  complicated  ])lexus  beset  with  varicosities.  These  tactile 
corpuscles  lie  in  the  papilla  of  the  corium  and  are  most  numerous  (23  to  one 
square  mm.)  in  the  skin  of  the  palm  of  the  hand,  the  finger-tips,  and  the  plan- 
tar surface  of  the  foot. 


X  150.     Techn.  No. 


Terminations  of  the  Motor  Nerves. 
The  meduUated  nerve-fibers  supplying  striated  muscle  divide  into  branches, 
and  these  subdivide  into  twigs  (nerve-fiber  bundles)  which  anastomose  and  form 
a  plexus,  the  intraniiisiular plexus.      In  the  vicinity  of  this  plexus  the  medul- 
lated    nerve-fibers    undergo    numerous  divisions,   so 
that  the  number  of  nerve-fibers  is  considerably  in- 
creased.    From  the  small  bundles  of  the  plexus  single 
delicate  nerve-fibers  spring,  each  one  of  which  finally 
unites  with  a  muscle-fiber.     At  the  point  where  the 
nerve-fiber  comes  into  contact  with  the  muscle-fiber 
it    loses    its    medullated    sheath,    the    axis-cylinder 
breaks  up  into  a  number  of  slightly  tortuous  terminal 
branches  with   bulbous,  swollen    extremities,  which 
form  the  so-called  motor  end-plafe,  which  rests  upon 
a  rounded,   finely-granular  disk-like  sole-plate  con- 
taining numerous  vesicular  nuclei.    Each  muscle-fiber 
possesses  at  least  one  motor  end-plate  ;  whether  these 
lie  upon  or  under  the  sarcolemma  is  not  yet  definitely  determined. 

The  nonmedullated  nerves  supplying  the  smooth  muscles  form  a  ground 
plexus  consisting  of  small  bundles  of  nerve-fibers ;  branches  of  this  plexus 
divide  repeatedly  and  form  networks,  the  intermediate  plexus,  from  which  small 


IG.    1 

[12.— Motor 

Nerve-End- 

ING 

IN  A  FiBEK  OF 

■  AN  Ocular 

Mur 

SCLE    OF     RaBI 

BIT        X    240 

N.    1 

Medullated  nei 

■ve-fiber:  K. 

nucl 

ei  of  the  disk. 

The  trans- 

vers 

e  stride  are  dis 

tinct  only  in 

the 

lower  half  of 

the   muscle- 

fibei 

•.     Techn,  No, 

,86  b. 

THE    SUPRARENAL    BOUV. 


bundles  of   fibrillae   arise  and   extend   to   the  muscle-fibers ; 
slightly  thickened  at  the  point  of  contact  with  the  muscle-fiber 


143 

they  are  often 


3.  THE   SUPRARENAL  BODY. 

The  description  of  the  suprarenal  body  with  the  organs  of  the  nervous 
system  is  warranted  by  the  profusion  of  its  nervous  elements,  by  its  relation  to 
the  central  nervous  system  as  established  by  experiment,  as  well  as  by  the  facts 
of  comparative  anatomy. 

Each  suprarenal  body  consists  of  a  cellular  parenchyma  and  a  connective- 
tissue  capsule,  which  sends  delicate  processes  into  the  interior  of  the  organ. 


Capsule. 


Tcchn.  No.  87.     B.  Sectiu 


X  50.     Tcchn.  No.  &9 


The  parenchyma  consists  of  an  outer  stratum,  the  cortex,  which  surrounds  an 
inner  mass,  the  medulla,  on  all  sides.  The  cortex  in  the  fresh  state  is  of  a 
yellow  color  and  is  composed  of  groups  of  cells  about  15  /x  in  size,  rounded  in 
shape,  posse.ssing  a  coarsely-granular  protoplasm,  sometimes  containing  fat  par- 
ticles, and  a  clear  nucleus.  According  to  the  arrangement  of  these  cells,  three 
zones  are  distinguished:  i,  the  Sf /w  glomcnilosa ;  2,  iht  zona  faseiciilafa  ;  3, 
the  zona  reticularis.  The  medulla  in  the  fresh  state  is  sometimes  lighter, 
sometimes  darker  than  the  cortex  ;  it  consists  of  polygonal  cells  possessing  a 
finely-granular  protoplasm  and  a  clear  nucleus,  which  are  arranged  in  oval 
groups  or  cords  joined  in  an  irregular  network. 


144  HISTOLOGY. 

In  the  outer  zone — zona  glomerulosa — the  cells  are  grouped  in  oval 
masses  ;  in  the  middle  zone — zona  fasciculata — -they  are  arranged  in  cylindrical 
columns,  and  in  the  innermost  zone  they  are  irregularly  scattered  in  anasto- 
mosing cords.     This  stratum  is  distinguished  by  its  pigment-cells. 

The  arteries  divide  in  the  capsule  into  numerous  branches,  which  penetrate 
the  cortex  and  there  form  a  long-meshed  capillary  netvi^ork,  which  passes  into 
the  medullary  substance  where  the  meshes  are  round.  From  the  latter  the  veins 
proceed,  of  which  the  larger  are  accompanied  by  longitudinally-disposed  bundles 
of  smooth  muscle-fibers.  While  still  within  the  medulla  the  veins  unite  and 
form  the  chief  vein,  the  suprarenal. 

The  numerous  nerves  (in  man  about  33  small  stems)  enter  the  corte.x  with 
the  arteries  and  pass  to  the  medullary  substance,  where  they  form  a  close  reticu- 
lum. They  are  nonmedullated  fibers,  chiefly  from  the  cceliac  plexus,  accompa- 
nied by  groups  of  ganglion-cells,  that  are  found  even  in  the  medulla. 


V.  THE  DIGESTIVE  ORGANS. 

MUCOUS  MEMBRANES. 
The  inner  surface  of  the  alimentary  tract,  of  the  respiratory  passages, 
parts  of  the  genito-urinary  system,  and  parts  of  the  organs  of  special  sense  are 
covered  by  a  soft,  moist  membrane,  the  mucous  membrane,  or  tunica  mucosa. 
It  is  composed  of  a  soft  epithelium  and  of  connective  tissue.  Immediately 
under  the  epithelium,  the  latter  is  usually  specialized  and  condensed  to  form  a 
structureless  membrane,  the  7ne!nbrana  propria  or  basement  membrane  ;  beneath 
this  follows  the  tunica  propria,  which  passes  by  a  gradual  transition  into  the 
subjacent,  loose-textured  tunica  submucosa,  which  in  turn  connects  the  mucous 
membrane  with  the  underlying  structures,  the  muscles  or  bones.  The  epithe- 
lium of  the  glands  is  derived  directly  from  the  epithelial  elements  covering  the 
mucous  membrane. 

The  Mucous  Membrane  of  the  Oral  Cavity. 
The  mucous  membrane  of  the  mouth  consists  of  two  parts:  (i)  the 
epithelium  and  (2)  the  tunica  propria;  beneath  the  latter  is  the  submucosa. 
The  epithelium  is  typical  stratified  squamous  epithelium.  The  tunica  propria 
is  formed  of  interlacing  connective-tissue  bundles  richly  interspersed  with 
elastic  fibers.  The  bundles  of  the  uppermost  strata  are  very  slender  and  form  a 
compact,  apparently  almost  homogeneous  feltwork.  The  surface  of  the  tunica 
propria  is  beset  with  numerous  usually  simple  papillae,  varying  greatly  in  height 
(Fig.  114).  The  highest  papillae  (0.5  mm.)  occur  at  the  edge  of  the  lips  and 
on  the  gums.  The  tunica  propria  passes  without  sharp  limits  into  the  submucosa, 
which  consists  of  somewhat  thicker  bundles  of  connective  tissue,  among  which 


THE    DIGESTIVE    ORCAXS. 


145 


the  elastic  fibers  are  not  numerous.  The  subinucosa  is  in  general  loosely 
attached  to  the  walls  of  the  oral  cavity  ;  only  on  the  gums  and  the  hard  palate  is 
it  firmer,  and  intimately  united  to  the  periosteum.  It  contains  the  glands  of  the 
mucous  membrane;  these  are,  with  the  exception  of  the  sebaceous  glands  occa- 
sionally found  at  the  edges  of  the  lips,  branched  tubular  mucous  glands  from  i 
to  5  mm.  in  size.  The  main  excretory  duct  is  somewhat  expanded  at  its  lower 
end  and  in  the  greater  part  of  its  extent  is  lined  with  stratified  scaly  epithelium  ; 
the  branches  and  twigs  into  which  it  divides  and  subdivides  are  lined  with  strati- 
fied squamous  and  simple  columnar  epithelium  respectively.  Not  infrequently 
the  main  excretory  duct  receives  the  excretory  tubes  of  small  accessory  glands 


Sf^.'^MAi^, 


Fig.  114.— Vbrticau  Section  THROUGH  THE  Mucous  Membrane  t)F  Lip  OF  Adult  Man.  X  3°.  '.  Papilla; 
2,  excretory  duct ;  the  hiinen  is  cut  open  at  one  point  only  ;  i,  accessory  gland  ;  4,  a  branch  of  the  excretory 
duct  in  transverse  section  ;  5,  gland-follicles  grouped  into  loDules  by  connective  tissue  ;  6,  a  gland-tubule  in 
:  section.    Techn.  No.  91. 


(Fig.  114,  2,  3).  The  minute  structure  of  the  gland-tubules  will  be  described 
with  the  glands  of  the  tongue.  The  numerous  blood-vessels  of  the  oral  mucous 
membrane  are  arranged  in  two  networks,  situated  in  two  planes,  of  which  the 
coarser  lies  in  the  submucosa,  the  capillary  network  in  the  tunica  propria.  From 
the  latter  terminal  capillary  loops  ascend  to  supply  the  apices  of  the  papillae. 
The  lyni/>h-vesse/s  also  form  two  networks,  a  coarser  in  the  submucosa,  a  finer  in 
the  tunica  propria.  The  medullated  nerve-fibers  form  a  wide-meshed  reticulum 
in  the  submucosa,  from  which  many  ramifying  fibers  ascend  to  the  tunica 
propria  where  they  terminate  in  endbulbs,  or  lose  their  medullary  sheath  and 
as  nonmedullated  nerve-fibers  penetrate  the  epithelium,  where  after  repeated 
division  they  terminate  in  free  endings  between  the  epithelial  cells. 


146 


HISTOLOGY. 


THE  TEETH. 
The  teeth  of  man  and  the  higher  animals  are  soHd  structures,  possessing  a 
central  cavity — tht  pulp-cavity — filled  with  a  soft  mass,  the  pi/ /p.  The  portion 
of  the  tooth  within  the  alveolus  or  socket  is  called  the/an^,  the  exposed  por- 
tion, the  crown;  the  juncture  of  these  portions  forms  the  neck ;  the  latter  is 
covered  by  the  gums.  The  hard  substance  of  the  tooth  consists  of  three 
different  parts:    (i)   the  dentine,  (2)  the   enamel  with  the  enamel  cuticle,  and 


Fig,  115. — Longitudinal  S 


Human  Tooth.     X  4-    Techn.  No.  92. 


(3)  the  cementum.  The  distribution  of  the  parts  is  as  follows :  the  dentine 
contributes  the  chief  bulk  of  the  tooth  and  determines  its  form  ;  it  completely 
encloses  the  pulp-cavity  except  where  a  small  nutrient  canal  at  the  apex  of 
the  fang  admits  the  numerous  blood-vessels  to  the  pulp ;  the  dentine  of  the 
crown  is  covered  by  the  enamel,  of  the  fang  by  the  cementum,  so  that 
its  surface  is  nowhere  exposed  (Fig.  115). 

The  dentine  or  i7<ory  is  a  white,  opaque  mass,  harder  than  bone.      It  con- 
sists of  an  apparently  homogeneous  ground-substance  composed  of  extremely 


THE    DIGESTIVE    ORGANS. 


147 


fine  fibrilla;,  and  is  pierced  by  numerous  minute  channels,  the  dentinal  tubules. 
The  latter  bt-gin  with  a  diameter  of  about  2.5  11  at  the  inner  surface  of  the  den- 
tine, describe  an  S-shaped  curve,  and  then  proceed  in  a  slightly  wavy  course, 
radially  directed  toward  the  outer  surface,  steadily  decrease  in  caliber,  and  ter- 
minate at  the  juncture  of  the  dentine  and  enamel  or  cementum,  or  thev  form  a 


«    A    LoNGITUniNAL    SbCTION    OF   THE    LaTRRAL     PaRT   Op   THE   C 

240.     I.    Uentinal  tubules,  extending  for  a  short  distance  into  the 
no,  3,  the  interglobular  spaces.     Techn.  No.  92 


A  Ht;MAN  Molar 
2,  dentinal  globules 


loop  and  turn  into  a  neighboring  tubule.  During  their  course  they  send  off 
numerous  lateral  branches  which  establish  communication  with  surrounding  cana- 
liculi.  The  matrix  immediately  surrounding  the  dentinal  tubules  is  especially 
dense,  and  forms  the  so-called  dentinal  sheaths.  The  lumen  of  the  dentinal  tubules 
is  occupied  by  the  dentinal  fibers.     At  the  periphery  of  the  dentine  are  the  inter- 


Cementum. 

UNAL    ShCTI<)N    op   the 
MuLAK     loOlH.        X    S40.        I. 

Tupted  by  a  granular  stratum, 
with  many,  2.  small  intcrt^l'ibnlar  spaces;  3,  bone- 
corpuscles  with  many  processes.     Techn.  No.  92. 


1  transverse  sectioi 
Techn,   No.  93. 


globular  spaces,  irregular  clefts  varying  in  size  and  filled  with  a  soft  mas'; ;  into 
these  spaces  the  dentine  juts  in  the  form  of  hemisi^herical  protuber;  nces,  the 
dentinal g.'obules.  At  the  neck  and  in  the  fang  are  many  very  smaL  inter- 
globular spaces,  which  form  the  so-called  granule  stratum  lying  immediately 
beneath  the  cementum. 


148 


HISTOLOGY. 


The  enamel  is  still  harder  than  the  dentine.  It  is  composed  exclusively 
of  long  hexagonal  homogeneous  columns,  3  to  6  /i  in  thickness — the  enamel 
prisms — which  are  firmly  united  with  one  another  by  a  scanty  amount  of  aque- 
ous cement-substance.  They  extend  radially,  with  many  undulations,  from 
the  surface  of  the  dentine  to  the  outer  surface  of  the  enamel ;  the  latter  is  cov- 
ered by  a  very  thin  but  very  resistant  membrane,  the  enatnel  cuticle  or  membrane 
of  Nasmyth. 

The  cemcntiim  (crusta  petrosa)  coincides  in  structure  with  bone.  It  con- 
tains many  Sharpey's  fibers.  Haversian  canals  are  found  only  in  the  cementum 
of  older  individuals;  stratification  in  the  lamells  is  seldom  well-defined. 
Bone-corpuscles  are  absent  near  the  neck. 

The  space  between  the  fang  and  the  alveolus  is  occupied  by  the  richly-inner- 
vated periosteum,  which  is  firmly  united  to  the  cementum  by  Sharpey's  fibers; 

they  penetrate  from  the  inferior 
maxilla  through  the  periosteum  into 
the  cementum.  The  uppermost  por- 
tion of  the  periosteum  is  called  the 
circular  dentinal  ligament. 

The  pulp  is  formed  of  a  soft 
connective  tissue  containing  deli- 
cate fibers,  not  united  into  bundles, 
and  whose  cellular  elements,  at  the 
surface  in  contact  with  the  dentine, 
form  a  layer  of  elongated  nucleated 
cells,  the  odontoblasts ;  these  send 
out  short  processes,  by  which  they 
connect  with  other  elements  in 
the  pulp,  and  long  processes  that 
extend  into  the  dentinal  tubules  as  the  above-mentioned  dentinal  fibers  (Fig. 
119/).      Blood-vessels  and  nerves  are  limited  to  the  pulp. 


Fig.  iig.— Six  Od 
/ :  p.  Pulp  processes 
240.     Techn.  No.  94. 


:  pulp  of  an  infant. 


Development  of  the  Teeth. 

The  development  of  the  teeth  in  man  begins  toward  the  close  of  the  second 
month  of  fetal  life,*  and  is  first  indicated  by  a  linear  proliferation  of  the  primi- 
tive epithelium,  which  in  the  form  of  a  continuous  projection  grows  obliquely  into 
the  subjacent  connective  tissue.  This  crest,  the  dental  ridge  (  "  enamel  germ  "  ) , 
develops  on  its  lateral  (labial)  surface  knob-like  protuberances,  the  dental 
bulbs,  which  correspond  in  number  to  the  temporary  teeth,  and  coincidently  in 
the  surrounding  mesoderm  as  many  conical  aggregations  of  closely-packed  con- 
nective-tissue cells  appear,  the  young  dental  papilla  (tenth  week).  The  latter 
advance  obliquely  from  the  labial  to  the  lingual  side  and  toward  the  surface,  and 


*  That  which,  at  an  earlier  period  (fortieth  day),  has  been  described  as  the  aniage,  is  not 
this  alone,  but  includes  the  aniage  of  the  labial  furrow. 


THE    DIGESTIVE    ORGAN'S. 


149 


are  embraced  by  the  dental  bulbs  in  such  a  manner  that  these  form  an  epithelial 
cap  for  the  dental  papillae.  Thus  each  bulb  becomes  an  enamel  organ.  At  the 
same  time  the  dental  ridge  has  assumed  a  more  nearly  vertical  position,  and  fol- 


Dent.->1  bulbs.     Denial  furrow. 


Dcnt.-il  ridge. 


Fig.  120. — Schematic  Reprbsbntation  op  thb  Initial  Procp.sses  in 
showing  the  formation  of  three  teeth.  The  anlage  of  each  anterior  t 
is  stippled,     k.   Free  edge  of  the  dental  ridge. 


lowing  the  direction  of  the  gums  a  longitudinal  groove  has  appeared,  the  dental 
f arrow, \\\)\c\\  indicates  the  line  along  which  the  dental  ridge  progressed  backward 
toward  the  mandibular  articulation.  The  time  of  the  appearance  of  the  dental 
furrow  varies  ;   it  is  frequently  present  in  the  initial  stages.      It  disappears  later. 


Dental  ridge  of 
upper  jaw. 


Fig.  121.— Frontal  Section  of  the  Head  op  an  Embryo  Sheep  4  cm.  long.     X  15.    Techn.  No.  95. 


The  original  broad  attachment  between  the  dental  ridge  and  the  enamel  organ  is 
diminished  by  partial  constriction,  and  is  finally  reduced  to  a  slender  cord,  the 
isthmus.    Meanwhile,  the  papilla  and  enamel  organ  have  developed  beyond  the 


150  HISTOLOGY. 

dental  ridge,  so  that  the  free  edge  of  the  latter  does  not  extend  to  half  the  depth  of 
the  enamel  organ  (Fig.  120  and  Fig.  123).  At  the  same  time  the  elements 
of  the  enamel  organ  undergo  differentiation.  The  inner  layer  of  cells,  resting 
upon  the  papilla,  develop  into  tall  columnar  elements,  the  inner  enamel-cells ;  their 
inner  surface  is  provided  with  acuticular  border.  The  outer  cells,  on  the  other 
hand,  steadily  decrease  in  height,  until  finally  they  are  reduced  to  thin  plates, 
the  outer  enamel-cells ;  the  cells  between  the  inner  and  outer  enamel-ceils,  by 
an  abundant  increase  of  the  intercellular  substance,  become  transformed  into 
stellate  anastomosing  elements,  and  form  the  enamel-pulp.  At  the  point  where 
the  inner  enamel-cells  bend  over  into  the  outer  layer,  the  enamel  organ  grows 
down  until  it  has  reached  the  extremity  of  the  anlage  of  the  tooth,  thus  form- 
ing, in  a  measure,  the  mould  or  matrix  in  which  the  tooth  develops.  The  deter- 
mination of  the  shape  of  the  future  tooth  is  the  first  function  of  the  enamel 


''^  e^^ —  "     r.    "'    -  Osseous  trabecuisc 

^^  U  V-'K  '      of  lower  jaw. 


Four  Months  Old.     X  42 


organ  ;  the  second,  the  production  of  the  enamel,  which  only  takes  place  in 
that  portion  of  the  inner  layer  covering  the  crown  of  the  tooth.  This  portion 
may  be  named  the  enamel  membrane.  Each  cell  of  this  membrane  deposits  a 
substance  which  subsequently  calcifies  and  becomes  an  enamel  prism.  The 
enamel-cells  surrounding  the  fang  take  no  part  in  the  production  of  the 
enamel ;  they  decrease  in  height  and  (as  here  the  enamel-pulp  soon  disappears) 
apply  themselves  directly  against  the  outer  enamel-cells,  the  two  layers  forming 
the  epithelial  sheath  of  the  fang  (Fig.  124). 

Before  the  production  of  enamel  has  begun,  the  first  lamina  of  dentine 
has  been  formed  (about  the  twentieth  week).  The  superficial  cells  of  the 
dental  papillae  elongate  and  become  the  odontoblasts,  the  agents  which  produce 
the  at  first  uncalcified  dentine.  These  cells  do  not  develop  beyond  the  extent 
of  the  epithelial  sheath.     As  soon  as  the  first  dentine  is  formed,  the  epithelial 


THE    DICESTIVE    ORGANS. 


151 


sheath  undergoes  retrogressive  change  ;  connective-tissue  ingrowths  from  the 
alveolar  periosteum  penetrate  between  the  epithelial  cells.  This  retrogression 
begins  at  the  lower  border  of  the  enamel  organ,  thus  severing  the  connection 
between  the  latter  and  the  deeper  parts  of  the  epithelial  sheath.  With  the 
completed  growth  of  the  tooth  the  last  remnant  of  the  epithelial  sheath  dis- 
appears. 

Even  before  the  production  of  enamel  and  dentine  the  connection  between 
the  dental  ridge  and  the  oral  epithelium  is  severed,  and  the  mesodermic  tissue 


% 


Thickened 
epilheliiiniof 


Upprr  Jaw  of  a 
Techn.  No.  95. 


surrounding  the  anlage  of  the  tooth  forms  a  compact  membrane,  the  dental 
sack,  in  which  subsequently  an  inner  looser,  and  an  outer  denser,  stratum  can  be 
distinguished.  =f=  The  enamel  cuticle  and  the  cementum  do  not  appear  until 
after  birth,  shortly  before  the  irruption  of  the  teeth.  The  former  is  produced 
by  the  merging  of  the  cuticular  borders  of  the  enamel-cells  into  a  firm  homo- 
geneous membrane  ;  the  latter  is  a  product  of  the  alveolar  periosteum. 


•The  dental  ridge  has  previously  become  a  perforated  plate,  beset  on  all  sides  with  short, 
j.igged  excrescences.  Remains  of  the  dental  ridge  may  be  found  in  the  gums  of  newborn  chil- 
dren, and  were  formerly  erroneously  regarded  as  glands  (glanduloe  tartarica;). 


152 


The  permanent  teeth  develop  in  the  same  manner  as  the  temporary  teeth  ; 
in  the  twenty-fourth  week  new  protuberances  develop  on  the  growing  ledge  of 
the  dental  ridge,  which  embrace  new  papillae  arising  from  the  sides.  The 
anlage  of  the  permanent  tooth  lies  at  first  in  the  same  alveolus  with  the  temporary 


Dental  papilla  (fut 


Blood-vessel. ' 
Bony  trabeculse  of  lo 


Fig.  124. — Longitudinal  Section 


;  42.     Techn.  No.  95. 


tooth  ;  a  separate  alveolus  is  developed  later.  The  completed  tooth  is  in  part 
of  epithelial  origin  (the  enamel),  and  in  part  derived  from  the  connective- 
tissue  dental  papilla  (the  dentine),  the  remains  of  which  persist  in  the  adult  as 
the  pulp.  The  cementum  is  in  a  measure  an  accessory  formation  contributed 
by  neighboring  tissues. 


THE    DIGESTIVE   ORGANS. 


153 


THE  TONGUE. 

The  bulk  of  the  tongue  is  formed  of  striated  muscles,  the  separate  bundles 
and  fibers  of  which  interlace  in  various  directions.  The  unattached  surfaces  of 
the  organ  are  covered  by  a  reflection  of  the  oral  mucous  membrane.  The 
bundles  of  the  muscular  tissue  are  disposed  in  three  planes  :  (i)  vertically, 
and  somewhat  radially  (geniohyoglossus,  lingualis,  and  hyoglossus)  ;  (2) 
transversely  (lingualis)  ;  and  (3)  longitudinally  (lingualis  and  styloglossus). 
Since  the  muscle-bundles  cross  one  another  for  the  most  part  at  right  angles 
sections  exhibit  a  regular,  beautiful  network.  A  median  septum,  the  septum 
lingua,  divides  the  muscular  tissue  into  a  right  and  a  left  half.  The  septum 
begins  at  the  hyoid  bone  and  gradually  increases  in  height,  reaching  its  great- 
est elevation  in  the  middle  of  the  tongue,  then  gradually  slopes  downward  and 


,  Srctios  op  t 
THE  Dorsum  op  the 
Human  Tongue.  X  30.  1.  Section  of  two 
filiform  papillae,  each  of  which  bears,  2,  three 
secondary  papillse :  3,  compound  :  4,  simple  pro. 
cess  of  epithelium,  the  surface  of  which  is  cov- 
ered with  masses  of  loosely-attached  scaly  epi- 
thelial cells. 


IG.     126.  —  LONGITUC 

iiNAL  Section 

OF    THE 

M 

ICOUS 

.Mem 
form 
4.  Sn 

papilla    w 
tail  filiform 

Hu 
ith, 
pap 

MAN 

lilla." 

Tongue. 
lecondary 
Techn.  N 

X    30. 
papillae ; 
0.96. 

I.  1 
3. 

sufk. 

forward  and  disappears  ;  it  does  not  extend  through  the  entire  half  of  the 
tongue,  but  ceases  at  a  distance  of  about  3  mm.  from  the  dorsum  of  the  organ. 
The  .septum  is  composed  of  compact  connective  tissue. 

The  mucous  membrane  of  the  tongue,  like  that  of  the  oral  cavity,  consists 
of  an  epithelium  and  a  tunica  i)ropria,  and  rests  on  a  submucosa.  It  is  char- 
acterized by  the  conspicuous  development  and  complicated  form  of  the  papillze. 
Three  kinds  of  papillae  are  distinguished  :  \\\q  filiform  or  conical,  the  fungiform , 
and  the  circumvallate  papillcE. 

The  filiform  papilla  are  cylindrical  or  conical  elevations  of  the  tunica 
propria,  bearing  on  the  summit  five  to  twenty  small  secondary  papillae.  They 
are  composed  of  distinctly  fibrillated  tissue  and  numerous  elastic  fibers,  and  are 
covered  by  a  thick  layer  of  stratified  scaly  epithelium  that  not  infrequently, 
over  the  secondary  papilla:,  forms  a  number  of  filamentous  horny  processes. 


154 


HISTOLOGY. 


The  filiform  papillae  are  very  numerous,  and  are  distributed  over  the  entire 
dorsum  of  the  tongue  ;  they  vary  in  height  from  0.7  to  3  mm.  (Fig.  125). 

The  fungiform  papillcE  are  rounded  elevations  connected  with  the  tunica 
propria  by  a  slightly-constricted  stalk  ;  their  entire  surface  is  beset  with  sec- 
ondary papillK.  They  consist  of  a  distinct  feltwork  of  connective-tissue 
bundles  which  contain  but  few  elastic  fibers.  The  epithelial  cover  is  thinner 
than  that  on  the  filiform  papilla  and  is  not  cornified.  The  fungiform  papillae 
are  also  distributed  over  the  entire  surface  of  the  tongue,  but  are  not  so  numerous 
as  the  filiform  ;  they  vary  in  height  from  0.5  to  1.5  mm.  They  are  usually 
easily  distinguished  by  their  red  color,  due  to  the  capillaries  shimmering  through 
the  transparent  epithelium  (Fig.  126). 

The  circumvallate papilla  resemble  broad,  flattened  fungiform  papillae,  and 
are  separated  from  the  surrounding  epithelium  by  a  circular  furrow  varying  in 
depth  and  bounded  by  a  ridge  designated  the  wall.     The  papillse  are  com- 


Secondar>  papilla 


Epitheliun  V    '^^ 


Taste- buds 

(inaistinci). 


X  30.     Techn,  No.  96. 


posed  of  connective  tissue,  like  that  of  the  fungiform  papillae.  Secondary 
papillae  are  found  only  on  the  upper  surface.  In  the  epithelium  covering  the 
sides,  and  occasionally  also  the  wall,  lie  the  end-organs  of  the  special  sense 
of  taste — the  taste-buds.  The  circumvallate  papillae  are  i  to  1.5  mm.  high  and 
I  to  3  mm.  broad.  They  are  eight  to  fifteen  in  number,  and  occur  on  the 
posterior  end  of  the  dorsum  of  the  tongue.  At  the  lateral  margins  of  the 
tongue,  just  in  front  of  the  anterior  pillars  of  the  fauces,  is  a  group  of  parallel 
folds  of  the  mucous  membrane — papilla  foliata — containing  numerous  taste- 
buds.     The  papillae  foliatae  are  especially  well  developed  in  the  rabbit. 

The  suhmucosa  at  the  tip  and  at  the  edges  of  the  tongue  is  firm  and  re- 
sistant and  intimately  connected  with  the  underlying  parts. 

The  Lymph-follicles  of  the  Tongue. — The  mucous  membrane  extend- 
ing from  the  circumvallate  papillae  to  the  epiglottis  is  peculiarly  modified  by 
the    development    of    lymph-nodules.     They   are   spherical    aggregations   of 


THE    DIGESTIVE    ORCANS. 


15s 


adenoid  tissue  1  to  4  mm.  in  size,  embedded  in  the  uppermost  strata  of  the 
tunica  propria,  and  form  easily  perceptible  macroscopic  elevations.  In  the 
center  a   punctate  opening  may  be  seen,  the  entrance  to  a  deep  central  crypt, 


I  Epilhelii 


128. — Vrrtical  Sfction  01 

<  20.     1    Cjyptof  Ihe  f.llicli 

mh  leucocyie>  on  the  Wt  .-ind  at  the  h:\~c.  :ilnir>sl  i 

aiiiing  ticrminal  centers  ;  y.  nodules  cm  through  th 

.  Kibrous  sheath.    5.  Section  of  excretory  duct  of 


THE  Root  of  thh  Tongue  of  Aiiult  Man. 
:ytes.  2.  Epithelium  of  the  crypt ;  infiltrated 
^n  the  right.  3,  Nodules  of  adenoid  tissue  con- 
le:  /•,  through  the  side:  /^,  at  the  periphery, 
gland.     6.   Blood-vessel.     Techn.  No.  96. 


lined  by  a  continuation  of  the  stratified  epithelium  of  the  oral  mucous  mem- 
brane. The  epithelium  bordering  the  crypt  is  surrounded  by  diffuse  adenoid 
tissue,  which  contains  a  variable  number  of  the  lymph-nodules,  with  germinal 
centers,  and  is  separated  by  a  sharp  line  of  demarcation 
from  the  subjacent  fibrillar  connective  tissue  of  the  tunica 
propria  ;  when  well  developed,  the  fibrous  bundles  of 
the  tunica  propria  are  circularly  disposed  about  the 
adenoid  tissue  and  form  a  fibrous  capsule  (Fig.  128,  4). 
Under  normal  conditions  numerous  leucocytes  of  the 
adenoid  tissue  wander  through  the  epithelium  into  the 
central  crypt  and  thence  to  the  oral  cavity ;  they 
are  readily  found  in  the  saliva,  as  "mucous"  and 
"  salivary  "  corpuscles.  The  epithelium  is  often  greatly 
expanded  in  consequence  and  destroyed,  or  is  infiltrated 
with  leucocytes  to  such  a  degree  that  its  boundary  can- 
not be  definitely  determined. 

The    Glands. — Two    kinds   of   branched    tubular 
glands  occur  in  the  mucous  membrane  and  in  the  super- 
ficial muscular  strata  of  the  tongue.    The  gland-cells  of  the  one  kind  produce 
a  mucigenous  secretion  (mucin)  ;  such  glands  are  named  mucous  glands.     The 
secretion  of  the  second  kind  is  a  thin,  watery,  serous  fluid,  distinguished  by  the 
large  amount  of  albumin  it  contains  ;  such  glands  are  called  serous  glands. 


Fig 

I?; 

,.— Fro 

M  A  Sbction 

TH 

llfOtJf.H     TH 

IE     Rc.OT     OF 

TH 

:b  ' 

lONGUH 

:   of    MoirSE. 

X 

90. 

A    s. 

erous    gland; 

th. 

:du 

ct-sysle 

m  silvered  by 
k  reaction/' 

Gi 

-Igi' 

s  "  blac 

th( 

Libular 

stniclMre     is 

ea: 

sily 

recogn 

ized.     Tech. 

156  HISTOLOGY. 

The  mucous  glands  are  of  the  same  structure  as  those  of  the  oral  mucous 
membrane,  and  occur  along  the  edges  and — in  larger  numbers — at  the  root 
of  the  tongue,  where  not  infrequently  their  excretory  ducts  open  into  the  crypts 
of  the  follicles.  The  ducts  are  lined  by  columnar  epithelium,  which  occasion- 
ally is  ciliated  ;  the  walls  of  the  tubules  consist  of  a  structureless  membrana 
propria  and  gland-cells  ;  the  latter  are  columnar  elements  possessing  a  firm  cell- 
membrane,  and  vary  in  appearance  with  their  functional  condition.  The  ex- 
hausted cell  is  smaller,  the  transverse-oval  nucleus  near  the  base  of  the  cell ; 
the  cell  loaded  with  secretion  is  broader,  and  the  nucleus  is  pressed  flat  against 
the  cell-wall.  Generally  the  same  gland,  often  the  same  tubule,  exhibits  vary- 
ing phases  of  secretion  ;  demilunes  are  however  not  formed  here,  because 
the  rigid  membrane  of  the  gland-cells  resists  the  pressure  exerted  by  neigh- 
boring cells.  Only  the  mucous  glands  of  the  tongue  of  the  cat  and  of  the 
uvula  of  man  exhibit  demilunes.  Nuhn's  glands  occurring  in  the  tip  of  the 
tongue  are  likewise  mucous  glands. 

The  serous  glands  are  limited  to  the  vicinity  of  the  papillae  circumvallatK 
and  foliatK  ;   the  excretory  ducts  open  into  the  furrows  between  the  papilla: 


•"■  d- 


N^ 


Fig.  130  — /,  //.  From  a  Section  of  a  Mucous  Gland  of  the  Root  of  Human  Tongue.  /.  Section  of  a 
tubule  with  (b\  gland-cells  empty  of  secretion,  and  (c)  gland-cells  filled  with  secretion  ;  d,  lumen.  //.  Cross- 
section  of  a  tubule  containing  only  cells  loaded  with  secretion.  ///  and  IV.  From  the  mucous  membrane  of 
the  tongue  of  rabbit.  ///.  Tubule  of  a  mucous  gland  in  transverse  section.  IV.  Several  tubules  of  a  serous 
gland,  at  rfthe  very  small  lumen.  V.  Several  tubules  of  a  human  serous  gland,  with  large  (af')  and  small 
\d)  lumen.    All  the  sections  are  magnified  240  times,     1  echn.  No.  96. 


and  the  wall,  and  are  lined  by  simple  or  stratified  columnar  epithelium,  not 
infrequently  ciliated.  The  tubules  consist  of  a  delicate  membrana  propria  and 
short  cylindrical  or  conical  cells,  destitute  of  a  membrane,  whose  dim  granular 
protoplasm  encloses  a  round  nucleus.  The  lumen  of  the  tubules  is,  especially 
in  animals,  very  narrow. 

The  blood-vessels  of  the  mucous  membrane  of  the  tongue  form  networks 
disposed  parallel  to  the  surface,  from  which  twigs  ascend  to  supply  the  papillae 
and  the  secondary  papillse.  At  the  root  of  the  tongue  small  arteries  pierce 
the  fibrous  envelopes  of  the  lymph-follicles,  and  break  up  into  capillaries  that 
penetrate  to  the  interior  of  the  nodules.  The  blood-vessels  of  the  glands  form 
networks  around  the  gland-tubules. 

The  lymph-vessels  of  the  tongue  are  arranged  in  two  sets  ;  a  deep  set  con- 
sisting of  larger  vessels,  and  a  superficial  set,  which  takes  up  the  lymph-vessels 
of  the  papillae.  The  lymph-vessels  at  the  root  of  the  tongue  are  very  numerous  ; 
they  form  networks  encircling  the  lymph-nodules. 

The  nerves  of  the  mucous  membrane  of  the  tongue,  the  glosso-pharyngeal 


THE    DIGESTIVE    ORGAN'S.  I57 

and  the  lingual  branch  of  the  fifth,  end  in  part  as  in  other  portions  of  the  oral 
mucous  membrane,  and  in  part  in  intimate  relation  with  the  taste-buds. 

THE  PHARYNX. 

The  wall  of  the  pharynx  is  composed  of  three  coats :  a  miiious,  a  muscular, 
and  2,  fibrous  coat.  The  mucous  coat,  like  the  oral  mucous  membrane,  possesses 
a  stratified  scaly  epithelium,  a  tunica  propria  beset  with  papillae,  and  also 
numerous  mucous  glands.  The  upper  or  respiratory  part  of  the  pharynx  is 
clothed  by  stratified  ciliated  columnar  epithelium  ;  the  lower  limit  of  the  latter 
is  variable.  Very  richly  developed  is  the  adenoid  tissue.  Between  the  pillars 
of  the  fauces  it  forms  conspicuous  accumulations,  one  on  either  side,  known 
as  the  tonsils,  which  in  respect  to  their  structure  in  man  and  many  animals 
correspond  to  an  aggregation  of  lymph-nodules  like  those  of  the  root  of  the 
tongue.  The  leucocytes  that  wander  through  the  epithelium  of  the  tonsils  are 
so  numerous  that  the  latter  may  be  regarded  as  the  most  fertile  source  of 
the  salivary  corpuscles.  The  adenoid  tissue  is  also  vigorously  developed  in 
the  respiratory  portion  of  the  pharynx,  where  on  the  posterior  wall  between  the 
orifices  of  the  Eustachian  tubes  it  forms  a  conspicuous  mass,  the  "  pharyngeal 
tonsil,"  which  agrees  in  its  structure  with  the  palatine  tonsils,  excepting  that 
the  lymphoid  tissue  is  less  sharply  circumscribed.  Here,  too,  many  leucocytes 
migrate  through  the  epithelium.  The  development  of  the  adenoid  tissue  of  the 
oral  cavity  and  of  the  pharynx  is  subject  to  considerable  variation. 

The  muscular  coat  (constrictor  muscles  of  the  pharynx)  consists  of  striated 
muscle-fibers,  the  description  of  which  belongs  to  the  province  of  macroscopic 
anatomy.  The  fibrous  tunic  is  a  stout  membrane  composed  of  a  dense  feltwork 
of  fibro-elastic  tissue.  Blood -ves.sels,  lymph-vessels,  and  nerves  are  distributed 
in  the  same  manner  as  in  the  oral  mucous  membrane. 

THE  ESOPHAGUS. 
The  walls  of  the  esophagus  comprise  a  mucous,  a  muscular,  and  a  fibrous 
coat.  The  mucous  coat  is  composed  of  a  stratified  squamous  epithelium,  of  a 
tunica  propria  beset  with  papillM,  and  following  thisof  a  stratum  of  longitudinally 
disposed  smooth  muscle-fibers,  the  muscularis  mucosa ;  subjacent  to  the  latter 
is  the  submucosa,  which  consists  of  loosely-joined  bundles  of  connective  tissue, 
and  in  the  upper  half  of  the  esophagus  contains  small  mucous  glands.  The 
muscular  tunic,  in  the  upper  portion  of  the  tube,  is  composed  of  striated  muscle- 
fibers,  which  in  the  lower  portion  are  replaced  by  smooth  muscle-fibers.  The 
latter  are  arranged  in  two  strata,  an  inner  circular  and  an  outer  longitudinal 
layer.  The  fibrous  coat  consists  of  compact  connective-tissue  bundles  inter- 
spersed with  numerous  elastic  fibers.  The  distribution  of  the  blood-vessels, 
lymph-ve.ssels,  and  nerves  is  the  same  as  in  the  jiharynx.  Between  the  circular 
and  the  longitudinal  layers  of  the  muscular  coat  the  nerves  form  a  plexus,  at  the 
nodal  points  of  which  minute  groups  of  ganglion-cells  occur  (see  Auerbach's 
[ilexus,  p.  170). 


iS8 


HISIOLOGY. 


THE  STOMACH. 
The  wall  of  the  stomach  is  2  to  3  mm.   tliick  and  comprises  four  coats  : 
a  mucous,  a  submucous,  a  muscular,  and  a  serous  or  fibrous  tunic. 


Fig.  131.— Fkom  a  Cross-Suction  of  the  Middle  Third  of  Human  Esophagus.  X  lo.  i.  Stratified 
squamous  epnheliuin.  2.  Tunica  propria.  3.  Muscularis  mucosa:.  4.  Submucosa.  5.  Circular  muscles. 
6.  Longitudinal  muscles,    g.  Blood-vessel.     Teclin.  No.  98. 


Epithelium      rtlf.^ 


\        Tunica  prop 


Fig.  132. — Transverse  Sec 
so  close  togeltier  that  its 
Techn.  No  99. 


[  Inner  circular 
!        layer  of  muscle 


^  Outer  longitiid  nal  .*"--,!      -- 

layer  of  mu^cle     I         -v^^-fj^. 


ble  onl)   at  the  b     c  of 


The  mucous  coat,  sharply  contrasted  with  the  white  esophageal  mucous 
membrane  by  its  reddish-gray  color,  consists  of  an  epithelium,  a  tunica  pro- 
pria, and  a  muscularis  mucosa;  (Fig.  132). 


THE    DIGESTIVE    ORGANS. 


159 


The  epithelium  is  a  simple  columnar  epithelium,  whose  elements  produce 
a  mucoid  secretion.     Two  zones  can  usually  be  distinguished,  an  upper  mucoid 


Epithelium  of  the  surface. 


1 


\  Gastric  pil  i 


Body. 


and  a  lower  proto])lasmic  ;   the  latter  contains  the  oval,  round,  or  flattened 
nucleus.     The  extent  of  the  mucoid  zone  varies  considerably  with  the  func- 


l6o  HISTOLOGY. 

tional  condition  of  the  cells.  After  the  discharge  of  their  mucoid  contents  the 
epithelial  elements  closely  resemble  goblet-cells.  The  tunica  propria  is  com- 
posed of  a  mixture  of  fibrillated  and  reticular  connective  tissue,  and  of  an  ex- 
tremely variable  number  of  leucocytes,  that  occasionally  lie  closely  aggregated 
and  form  solitary  lymphatic  nodules.  The  tunica  propria  contains  so  many 
glands  that  its  tissue  is  limited  to  delicate  septa  between,  and  to  a  thin  stratum 
below,  the  tubules.  In  the  pyloric  end  the  glands  are  far  apart,  the  tunica 
propria  is  conspicuously  developed,  and  not  infrequently  elevated  in  filamentous 
or  leaf-like  villi. 

Two  kinds  of  gastric  glands  are  recognized  :  fundus  glauds,'^^  situated 
chiefly  in  the  middle  and  cardiac  thirds  of  the  stomach,  and  pyloric  glands,  con- 
fined to  the  narrow  pyloric  region.  Both  kinds  are  simple  tubular  glands, 
often  branched,  especially  in  the  pyloric  region,  and  open  singly  or  in  groups 
into  minute,  pit-like  depressions  in  the  mucous  membrane  of  the  free  surface. 
The  portion  of  the  gland  adjoining  these  depressions  is  called  the  neck,  the 
following  portion  the  body,  and  the  blind  end  the  fundus  (Fig.  133).  Each 
gland  consists  of  a  membrana  propria  and  of  gland-cells. 

The  fundus  glands  contain  two  kinds  of  cells:  cliief-  or  central-cells  and 
parietal-  or  (?(7(/-cells.      The  former  are  clear,  cubical  or  short  columnar  cells. 

Portion  of  a  parietal-cell. 

Parietal-cell  adjoining  a  lateral  \'^  ,,  n. 

branch  of  the  lumen. 

^-^-■' 

Fig.  134. — Transverse  Section  of  a  Human  Fundus  Gland.     X  240.     Techn.  No.  102. 

whose  granular  protoplasm  surrounds  a  spherical  nucleus.  The  chief-cells  are 
very  unstable.  The  parietal-cells  are  marked  by  their  affinity  for  anilin  dyes, 
with  which  they  react  intensely.  The  two  kinds  of  cells  are  not  equally  dis- 
tributed;  the  chief-cells  form  the  principal  portion  of  the  fundus,  the  parietal- 
cells  are  irregularly  distributed,  but  are  especially  numerous  in  the  neck  and  the 
body  of  the  tubule.  Here  they  lie  in  rows  beside  the  chief-cells,  but  toward 
the  fundus  they  are  pressed  to  the  periphery,  without,  however,  being  shut  off 
from  the  lumen,  with  which  they  communicate  by  a  short  lateral  canal  e.xtend- 
ing  between  the  chief-cells  from  the  lumen  to  the  parietal-cells.  The  lateral 
canal  is  the  only  one  of  the  system  of  canaliculi  enveloping  the  parietal-cells 
that  can  be  seen  in  ordinary  preparations.  By  the  aid  of  Golgi's  "  black  re- 
action," which  also  blackens  the  secretion,  it  may  be  seen  that  from  the  axial 
lumen  of  the  fundus  glands  minute  lateral  twigs  branch  off  at  right  angles, 
divide  and  anastomose,  forming  a  fine-meshed  network  of  "  secretory  capil- 
laries" that,  basket-like,  embrace  each  parietal-cell.  The  secretion  is  discharged 
from  all  sides  of  the  cell,  passes  into  the  secretory  capillaries,  then  into  one  or 


*  In  the  earlier  text-books  the  fundus  glands  were  called  peptic  glands,  a  name  based  upon 
,  function  of  the  glands  now  called  into  question. 


THE    UKJESTIVK    ORGANS. 


i6i 


more  short  lateral  canals,  and  finally  into  the  lumen  of  the  gland  (Fig.  i6 
and  Fig.   135). 

The  assertion  upheld  on  various  sides  that  the  chief-  and  the  parietal-cells 
are  different  functional  appearances  of  one  kind  of  cell,  as  also  the  statement 
that  during  digestion  the  parietal-cells  multiply,  but  disappear  after  prolonged 
fasting,  are  very  much  in  need  of  thorough  investigation.  The  stomach  of  an 
animal  killed  after  a  long  winter  hibernation  still  contains  parietal-cells. 

The  pyloric  glands  are  furnished  almost  throughout  with  columnar  cells 
containing  a  spherical  nucleus  situated  near  the  ba.se  of  the  cell,  which  in  the 


rr^s^.f\ 


Tunica  propria 
with  gLinds. 


FlC.   135. — CkOSS-SBCTION  THROUGH  THR  M  IICOUS  MbMBRANH  OP  THE  FONDOS  OF  StOMACH  OP  MOUSB  (DURING 

DlGKSTloN).  X  234.  In  'he  gland  to  the  right  the  entire  system  of  canjiliculi,  in  the  other  glands  only 
a  portion  of  the  same,  is  silvered.  The  "  baskets  "  formed  by  the  secretory  capillaries  can  be  distinguished. 
Tcchn.  No.  iiy. 


intermediate  zone,  that  is,  the  border  zone  between  the  pyloric  and  the  fundu.s 
mucous  membrane,  resemble  very  closely  the  chief-cells,  with  which  they  have 
been  compared.  In  man  isolated  parietal-cells  are  found;  in  animals,  e.g., 
the  dog,  a  few  dark  conical  cells  occur,  that  owe  their  appearance  to  the  com- 
pression e.xerted  by  neighboring  cells. 

The  foregoing  description  applies  to  the  stomach  as  seen  after  a  period 
of  fasting  ;  during  digestion  the  parietal-cells  are  larger,  the  chief-cells,  as  also 


l62 


HISTOLOGY. 


the  cells  of  the  pyloric  glands,  are  darker,  the  nuclei  of  the  latter  are  nearer  to 
the  middle  of  the  cell,  and  the  secretory  capillaries  expanded  with  increased 
contents  are  wider  than  in  the  fasting  organ. 

The  miiscularis  mucosce  consists  of  smooth  muscle-fibers  arranged  in  two 
or  three  layers  interlacing  in  various  directions,  from  which  single  strands 
branch  off"  and  ascend  vertically  between  the  gland-tubules  (Fig.  133). 

The  stibmttcosa  is  composed  of  loosely-united  connective-tissue  bundles 
and  elastic  fibers,  and  occasionally  contains  small  clusters  of  fat-cells. 

It  is  only  in  the  pyloric  region  that  two  separate  layers  can  be  distinguished 
in  the  muscular  coat,  a  thicker  inner  circular  and  a  thinner  outer  longitudinal 
layer.  In  the  other  regions  of  the  stomach  the  arrangement  of  the  muscle- 
tissue  is  very  comijlicated,  owing  to  the  extension  of  the  muscular  strata  of  the 
esophagus  to  the  stomach,  as  well  as  by  the  curving  of  the  organ  that  ensues  in 
the  course  of  development ;  sections  exhibit  bundles 
of  fibers  extending  in  every  possible  direction. 

The  serous  coat  will  be  described  with  the  peri- 
toneum. 

THE  INTESTINES. 
The  wall  of  the  intestines,  like  the  stomach,  is 
composed  of  four  tunics ;  a  mucous,  a  submucous,  a 
muscular,  and  a  serous. 

The  mucosa  is  thrown  into  folds,  the  valvulse 
conniventes,  especially  well  marked  in  the  upper  part 
of  the  small  intestine,  the  object  of  which  is  to  in- 
crease the  superficial  extent  of  the  membrane.  In 
addition  to  these  readily  perceptible  plications  there 
are  still  other  contrivances  serving  a  similar  purpose, 
that  stand  at  the  limit  of  macroscopic  perception.  These  are  minute  ele- 
vations and  depressions  of  the  raucous  membrane.  The  former,  the  villi, 
are  present  only  in  the  small  intestine ;  in  the  large  intestine  of  man  they 
are  wanting;  they  are  processes  about  i  mm.  high,  in  the  duodenum  of  leaf- 
like, in  the  remainder  of  the  small  intestine  of  cylindrical  form.  The 
depressions  begin  at  the  pylorus,  and  are  found  throughout  the  whole  length  of 
the  intestine.  They  occur  in  their  most  primitive  form  in  fishes,  and  originate 
in  parallel  folds  running  lengthwise  that  are  connected  by  small  transverse  folds. 
In  vertical  sections  these  shallow  depressions  appear  as  short,  wide  sacks,  called 
crypts.  In  mammals  the  crypts  are  deeper,  their  lumen  narrower,  and  placed  in 
rows  close  beside  one  another  they  have  the  appearance  of  simple  tubular 
glands ;  but  they  could  only  be  regarded  as  such  if  the  epithelial  cells  lining 
them  produced  a  specific  secretion,  which  is  not  the  case.  Whether  the  isolated 
granular  cells  that  occur  in  the  fundus  of  the  crypts  are  gland-cells  is  a  question. 
The  crypts  are  known  as  the  follicles  or  cr)'pts  of  Licberkiilin. 

The  mucous  membrane  consists  of  an  epithelium,  a  tunica  propria,  and 
a  muscularis  mucosae.     The  epithelium,  which  clothes  the  entire  free  surface, 


THE    MUCOU 

OF  Human  St 
X  240.    Techn.  No.  lo: 


THE    DIGESTIVE    ORGANS. 


163 


including  the  villi,  and  lines  the  crypts  is  a  simple  columnar  epithelium,  the 
elements  of  which  in  their  mature  condition  consist  of  a  granular  protoplasm 
containing  numerous  resorbed  fat-particles,  a  usually  oval  nucleus,  and  a  cell- 
membrane.  On  the  free  surface  of  the  cells  there  is  a  homogeneous  or  finely- 
striated  iasa/  iion/er  chaTa.cteTht\c  of  the  intestinal  epithelium. 

The  regeneration  of  the  epithelium  takes  place  only  in  the  crypts  of 
Lieberkuhn,  where  by  mitotic  division  new  cells  are  constantly  formed,  which 
gradually  move  upward  and  replace  the  cells  that  disintegrate  on  the  upper' 
surface  of  the  mucous  membrane.     Therefore  the  youngest  generation  of  epi- 


Fic.  137. — Longitudinal  Section  op  thr  Jejuncm  op  Adult  Man.  X  i6-  The  circular  fold  (valvula 
conniventcs)  on  the  right  supports  two  small  solitar)'  nodules,  that  do  not  extend  into  the  submucosa,  and  of 
which  the  left  exhibits  .-%  germinal  center,  X.  The  epithelium  is  slightly  loosened  from  the  connectiv 
core  of  many  of  the  villi,  so  that  a  clear  space,  X  X,  exists  between  the  two.  The  isolated  bodies  lying  r 
the  villi  (more  numerous  to  the  left  of  the  valvtilz  conmventes)  are  partial  sections  of  villi  that  were  bent, 
therefore  not  cut  through  their  entire  length.     Techn.  No.  105. 


thelial  cells  is  found  in  the  crypts,  the  oldest  on  the  free  upper  surface — in  the 
small  intestine  on  the  apices  of  the  villi.  Goblet-cells  in  extremely  variable 
numbers  occur  in  the  intestinal  epithelium ;  they  possess  an  elliptical  or,  not 
infrequently,  a  chalice  form  ;  the  upper  portion,  that  directed  toward  the 
surface  of  the  intestine,  undergoes  different  degrees  of  distention  as  the  proto- 
plasm is  transformed  into  mucus,  and  the  nucleus  with  the  remainder  of  the 
unaltered  protoplasm  lies  at  the  base  of  the  cell ;  a  basal  border  is  wanting,  in 
place  of  which  a  sharply-defined  circular  orifice  is  found,  through  which  the 
mucus  is  p>oured  out  on  the  surface  (Fig.  139,  A). 


164 


HISTOLOGY. 


The  goblet-cells  are  derived  from  the  ordinary  epithelial  cells  of  the  in- 
testine. In  certain  conditions  each  young  intestinal  epithelial  cell  may  assume 
the  functions  of  a  aroblet-cell. 


Tangential  sections 

ofvilli.      , 

I 


Eplthelii 


Tunica 
piopri 


Lieberkiihn's  crypts. 


Oblique  sections  of  Lieberkiihn 


rypts. 


Fig.  138. — Section  of  thb  Mucous  Mbmbrane  of  Jeju.num  op  .Adult  Man.  X  80.  The  empty  space, 
a,  between  the  tunica  propria  and  the  epithelium  of  the  villi  is  an  artificial  product,  the  result  of  the  shrink- 
ing action  of  the  fixing  fluid.  Not  infrequently  within  the  space  lie  cells  that  have  been  pressed  out  of  the 
tunica  propria.  In  its  retraction  the  epithelium  often  tears,  and  then  the  villus  appears  to  have  an  opening, 
d,  at  its  apex.    The  goblet-cells  have  been  sketched  on  one  side  of  the  villus  to  the  right.    Techn.  No.  105. 

The  several  phases  of  secretion  appear  in  regular  sequence,  and  so  that  the 
later  phases  are  always  to  be  seen  in  the  apices  of  the  villi  or  near  the  upper 
surface  of  the  mucous  membrane,  the  initial  phases  in  the  crypts  of  Lieberkiihn 
(Fig.  140). 


Fig.  139. — Intestina 


piTHELiuM.  X  560.  A.  Isolated  goblet-cells  of  rabbit.  Techn.  No. 
a  section  of  the  mucous  membrane  of  human  intestine.  Techn.  No. 
r  cells. 


X.   Escap- 
A  goblet- 


Ill  the  crypts  of  the  small   intestine  the  number  of  goblet-cells  is  propor- 
tionatel}'  less  than  in  the  large  intestine  ;   this  is  explained  by  the  fact  that  the 


THE    DIGESTIVE    ORGANS. 


165 


young  epithelial  cells  of  the  crypts  move  more  rapidly  to  the  surface,  the  greater 
superficies  of  the  small  intestine,  so  much  increased  by  the  villi,  necessitating 
a  greater  supply  of  young  cells  to  replace  those  that  disintegrate  on  the  surface  ; 
the  elaboration  of  mucus  often  does  not  take  place  in  the  crypts,  but  first  begins 
in  the  cells  on  the  villi.  In  the  large  intestine,  where  the  villi  are  absent,  the 
passage  to  the  surface  takes  place  slowly,  and  the  cells  have  time  to  produce 
secretion  while  they  are  within  the  crypts.  Out  of  this  arose  the  misconcep- 
tion that  the  crypts  of  the  small  intestine  produced  a  serous  fluid ;  those  of  the 
large  intestine  a  mucoid  secretion. 

Between  the  epithelial  cells  migratory  leucocytes  from  the  underlying  tunica 
propria  are  found  in  varying  numbers. 


. 

-  Tunica  propria. 

^         ?           -7  .         S      -J     t,          .      ^ 

'^iU-v^i' 

l'"rtion  ot  a  capilUrj' 

f*/^^           V€^'^:i"     ; 

Mood- vessel 

■  **  ^        '      )     C^   _  jBi  1 

§^  •%.  *^«  '-'-- 


N'jcleus  of  a  wandering 
leucocyte. 


Tangential  section  of  a 
goblet-cell. 


't 


'Y\it.  tunica  propria  consists  chiefly  of  fibrillated  and  reticular  connective 
tissue  which  contains  an  e.xtremely  variable  number  of  leucocytes.  Owing  to 
the  numerous  crypts  present  the  tunica  propria  of  the  large  intestine  is  confined 
to  the  spaces  between,  and  to  a  narrow  zone  below,  the  tubules,  as  in  the 
stomach  ;  throughout  the  small  intestine  the  tunica  propria  extends  into  the 
villi. 

The  muscularis  miicosiz  consists  of  an  inner  circular  and  an  outer  longi- 
tudinal   layer  of  smooth   muscle-fibers.     Fibers  derived   from   the   muscularis 


1 66 


HISTOLOGY. 


mucosae  extend  within  each  vilhis  nearly  to  its  apex.     Their  contraction  effects 
a  shortening  of  the  villus. 

The  submiuosa  consists  of  loose  fibrous  connective  tissue,  and  in  the 
upper  half  of  the  duodenum  contains  branched  tubular  glands — the  glands  of 
Brunner.  The  excretory  ducts  of  these  glands  are  clothed  with  columnar  cells, 
pierce  the  muscularis  mucosje,  and  run  in  the  tunica  propria  parallel  with  the 
crypts  of  Lieberkiihn.  The  walls  of  the  tubules  are  formed  of  columnar 
gland-cells  and  a  structureless  membrana  propria. 

The  Lymph-nodules. 
It  has  been  previously  mentioned  that  the  tunica  propria  of  the  mucous 
membrane  contains  leucocytes  or  lymphoid  cells  in  variable  numbers,  occurring 


Lieberkiihn's  crypls.  -==*- 


Ganglion-cells  of  Auerbach's  pie 


left. 


;.  141. — Longitudinal  Section  thkough  the  Duodb 
loosened  from   the  connective  tissue  of  the  villus  on  the 
cut  obliquely.     The  epithelium  has  fallen  from  the  middle  villus,  s 
posed.     The  serosa  is  represented  by  a  line  beneath  the  longitudi 


cular  layer.  J 

Cat.     X  30.     The  epithelii 

The  two  villi  at  the  ex 

that  the  ccnnective-tiss 

l1  layer  of  the  muscular 


either  as  diffuse  adenoid  tissue  or  a.s  circumscribed  masses  0.5  to  2  mm.  in  size. 
The  latter  are  lymph-nodules  which  occur  singly  as  the  solitary  nodules  (soli- 
tary follicles)  or  in  groups  as  Peyer' s  patches. 

The  solitary  nodules  vary  greatly  in  number  in  the  gastric  mucous  mem- 
brane ;  they  are  more  numerous  in  the  intestines.  They  usually  possess  an 
oval  form,  and  in  the  beginning  of  their  development  always  lie  in  the  tunica  pro- 
pria, close  under  the  epithelium,  with  their  base  directed  toward  the  muscularis 
mucosae.  With  advancing  growth  (in  cats  at  birth)  they  break  through  the 
muscularis  mucosEE  and  expand  in  the  submucosa,  where  the  loose  tissue  offers 
but  little  resistance.  The  part  of  the  nodule  lying  in  the  submucosa  has  a 
spherical  outline,  and  soon  becomes  considerably  larger  than  that  within  the 
tunica  propria.     The  completed  solitary  nodules,  therefore,  are  in  general  pear- 


THE    DIGESTIVE    ORGANS. 


167 


shaped,  with  the  small  end  turned  toward  the  epithelium.  Where  the  nodules 
are  situated  the  villi  are  wanting  and  the  crypts  are  pushed  aside.  The  solitary 
nodules  are  composed  of  adenoid  tissue  and  usually  contain  a  germinal  center. 
The  young  leucocytes    formed    in    them    pass    in    part  into    the  neighboring 


Of  muscularis. 
The  . 


Patch  of  Pbvrr  or  thb  Small  Intbstinb  of  Cat. 
■ilhin  the  pl.lne  of  the  section.     X  '»■     Techn.  No.  107. 


*^i^i<sn;^'^ 


Fig.  143.— From  a  Srction  op  thr  Small  Intbstinb  op  a  Sevbn-Days'-Old  Kr 
solitary  follicle.  The  epithelium  on  the  left  contains  many  wandering  leucocyte: 
right  contains  but  three  leucocytes.     Techn.  No.  107. 


EN.     X  950.    Crest  of  a 
The  epithelium  on  the 


lymph-vt'ssels,  and  in  part  wander  throngh  the  epithelium  into  the  intestine. 
'I'he  columnar  epithelium  covering  the  apex  of  the  nodules  contains  wandering 
leucocytes  (Fig.  143). 

The  />ii/c/ies  of  Peyerzx^  groups  of  ten  to  sixty  nodules  that  lie  side  by 
side,  never  over  one  another,  each  of  which  has  the  structure  of  a  solitary 


i68 


HISTOLOGY. 


nodule.  Occasionally  the  outline  of  an  individual  nodule  is  altered  by  the 
pressure  of  adjacent  nodules  (Fig.  142).  They  occur  principally  in  the  lower 
portion  of  the  small  intestine,  and  are  either  isolated  from  one  another  or 
embedded  in  diffuse  adenoid  tissue,  in  which  case  only  the  germinal  centers 
can  be  distinguished.  This  is  not  infrequently  the  case  in  the  vermiform 
process  of  man. 

The  muscular  layer  of  the  intestine  consists  of  an  inner  robust  circular, 
and  an  outer  thinner  longitudinal  stratum  of  smooth  muscle-fibers.  In  the 
large  intestine  the  longitudinal  muscular  layer  is  only  well  developed  at  the 
folds  corresponding  to  the  intervals  between  the  sacculi ;  between  these  folds  it 
is  extremely  thin. 

The  structure  of  the  serosa  will  be  described  with  the  Peritoneum. 


Lymph-follicle 


Circular  muscles. 
Longitudinal  muscles. 


Artery. 


;.  144.— From  a  Cross-Sbction  of  an  Injected  Small  Intestine  of  Rabbit.  X  5°-  Th":  lymph-nodule 
is  sectioned  so  that  in  the  upper  half  the  superficial  capillary  network  is  visible,  in  the  lower  half,  the  capil- 
lary loops  occurring  within  the  interior  of  the  nodule  The  section  is  thick  and  unstained,  and  the  crypts 
of  Lieberkuhn  cannot  be  distinguished,  i.  The  network  of  blood-vessels  within  the  muscularis;  2,  within 
the  submucosa  ;  3,  within  the  tunica  propria.     Techn.  No.  110. 


The  Blood-vessels  of  the  Stomach  and  Intestines. 
The  blood-vessels  of  the  stomach  and  the  large  intestine  have  a  precisely 
similar  distribution,  which  is  modified  in  the  small  intestine  by  the  presence  of 
the  villi.  In  the  stomach  and  the  large  intestine  the  entering  arteries  first  give 
off  small  branches  to  the  serosa,  then  pierce  the  muscularis,  which  they  also 
supply,  and  form  in  the  submucosa  a  network  extending  parallel  to  the  sur- 
face. From  this  small  twigs  ascend  through  the  muscularis  mucosa,  and  in  the 
tunica  propria  at  the  base  of  the  glands  form  another  network  parallel  to 
the  surface.     Fine  capillaries  (4.5  to  9  ix  wide)  arise  from  the  latter,  and  form 


THE    DIGESTIVE    ORGANS.  1 69 

plexuses  surrounding  the  gland-tubules  and  crypts;  wider  capillaries  (9  to  iS 
!i)  form  a  subepithelial  plexus,  which  lies  wreath-like  about  the  mouths  of  the 
glands.  Venules  take  their  origin  from  the  wide  capillaries,  pass  vertically 
down  between  the  gland-tubules,  and  of)en  into  a  venous  plexus  lying  parallel 
to  the  surface  in  the  tunica  propria  ;  in  their  further  course  the  veins  run  along- 
side the  arteries.  The  veins  arising  from  the  venous  plexus  in  the  submucosa 
are  furnished  with  valves  to  the  point  where  they  meet  the  veins  of  the  small 
intestine  approaching  along  parallel  paths.  The  larger  branches  and  the  trunk 
of  the  portal  vein  are  without  valves. 

In  the  small  intestine  only  the  arteries  supplying  the  crypts  are  distributed 
in  the  same  manner  as  in  the  large  intestine.  A  special  artery  passes  to  the 
base  of  each  villus  (more  than  one  when  the  villus  is  wide),  breaks  up  into  a 
capillary  network  extending  beneath  the  epithelium,  and  terminates  in  a  venous 
stem  which  descends  almost  vertically  to  the  mucosa,  taking  up  in  its  course 
the  capillaries  from  the  crypts.  In  the  dog  the  artery  enters  the  villus  along- 
side the  vein  ;  it  then  breaks  up  into  a  subepithelial  capillary  plexus,  that 
passes  vertically  or  obliquely  to  the  long  axis  of  the  villus  over  into  the  vein. 
The  further  course  of  the  veins  is  the  same  as  in  the  large  intestine. 

The  duodenal  glands  (glands  of  Brunnerj  are  enveloped  in  a  capillary 
plexus  supplied  by  the  blood-vessels  of  the  submucosa. 

The  lymph-nodules  are  surrounded  by  a  superficial  capillary  network, 
from  which  fine  capillaries  extend  into  the  interior ;  often  these  do  not  pene- 
trate to  the  center,  which  is  then  without  blood-vessels  (Fig.  144). 


The  Lvmph-ve.ssels  of   the   Sto.m.\ch  and  the  Intestines. 

The  lymph-  (chyle)  vessels  of  the  stomach  and  the  large  intestine  begin 
in  the  mucous  membrane  as  blind  capillaries  about  30  ;i  wide,  and  descend 
between  the  gland-follicles.  In  the  mucous  membrane  of  the  small  intestine  the 
lymph -\-essels  begin  in  the  a.\es  of  the  villi ;  in  cylindrical  villi  they  are  simple 
(in  leaf-shaped  villi  multiple)  canals(27to  36  ;u  wide)  closed  at  their  upper  ends 
— lymph-radicles  or  lacteals.  All  these  vessels  descend  to  a  narrow-meshed 
capillary  plexus  lying  at  the  base  of  the  glands  and  extending  parallel  to  the 
surface,  which  communicates  by  numerous  anastomoses  with  a  wide-meshed 
plexus  in  the  submucosa ;  the  lymph-vessels  proceeding  from  this  network 
l^enetrate  the  muscular  coat  and  take  up  the  vessels  of  a  plexus  lying  between 
the  circular  and  the  longitudinal  muscular  strata,  called  the  intramuscular 
lymphatic  plexus,  which  takes  up  the  lymph-capillaries  of  both  muscular 
layers.  The  vessels  then  run  beneath  the  serosa  to  the  edge  of  the  mesentery 
and  pass  onward  between  its  folds.  Many  of  the  vessels  are  provided  with 
valves. 

In  certain  localities  the  course  of  the  lymph-vessels  in  the  mucosa  is  modi- 
fied ;  the  nodules  of  the  patches  of  Peyer  never  contain  h-mph-vessels.  They 
press  aside  the  capillaries,  which  run  in  the  interstices  between  them,  constantly 
decreasing  in  number  but  increasing  in  caliber.      It  is  probable  that  the  lymph- 


170 


HISTOLOGY. 


sinuses  of  the  rabbit  (p.  97)  are  nothing  else  than  immensely  widened,  flat- 
tened capillaries. 

The  Nerves  of  the  Stomach  and  the  Intestines. 
The  numerous  nerves,  consisting  mainly  of  gray  fibers,  form  a  plexus  be- 
neath the  serosa,  then  penetrate  the  longitudinal  layer  of  the  muscular  tunic 
and  between  this  and  the  circular  layer  are  arranged  in  a  conspicuous  network, 
the  intramuscular  ganglionic  plexus  or  Auerbacli  s  plexus  ;  numerous  groups  of 
multipolar  ganglion-cells  are  found  along  the  course  of  the  nerves,  usually  at 
the  nodal  points  of  the  network,  the  meshes  of  which  are  angular  or  elliptical. 
From  this  network  bundles  of  pale  fibers  are  given  off,  usually  at  right  angles, 
which  in  part  supply  the  longitudinal  and  the  circular  strata  of  the  muscular  tunic, 
while  another  portion  pierces  the  latter  and  enters  the  submucosa.    In  the  muscu- 


FiG.  145. — A.  Surface  View  of  Auebbach's    Plexus  of  Infant 
r,  layer  of  circular  muscle-fibers,  recognized  by  their  rod-shaped  n 

B.  Surface  View  of  Meissner's  Pi.e.\us  of  the  Same  Infant. 
blood-vessel  shimmering  through  the  overlying  tissue,     'I'echu.  No 


X  50.     s^.  Groups  of  ganglion-cells  ; 
lei.     Techn.  No.  in  a. 
'  50.    g.  Groups  of  ganglion-cells ;    b, 


lar  coat  the  nerves  form  a  rich  rectangular-meshed  network,  from  which  nerve- 
fibers  turn  aside  and  after  repeated  division  approach  the  muscle-fibers,  on 
which  (not  within)  they  terminate  in  free  club-shaped  endings.  The  nerves 
in  the  submucosa  form  a  delicate  ple.xus,  Meissner's  plexus,  whose  meshes  are 
narrower  and  whose  groups  of  ganglion-cells  are  smaller.  From  this  spring 
numerous  fibers  which  enter  the  tunica  propria,  and  in  part  weave  a  nervous 
net  about  the  crypts,  and  in  part  enter  the  villi,  where  they  terminate  free  in 
the  parenchyma  or  close  beneath  the  epithelium,  without  connection  with  the 
epithelial  cells. 

A  network  corresponding  to  the  intramuscular  ganglionic  ple.xus  occurs 
between  the  layers  of  the  muscular  coat  of  the  esophagus. 


THE    DIGESTIVE    ORGANS. 


171 


THE  SALIVARY  GLANDS. 

The  salivary  glands  are  the  submaxillary,  the  sublingual,  the  parotid,  and 
the  pancreas.  They  are  compound  tubular  glands,  which  elaborate  either  a 
mucoid  or  a  serous  fluid  rich  in  albumin,  or  both  the  mucoid  and  the  serous 
secretion,  .\ccordingly  we  distinguish  :  (i)  mucous sa/irarv ^/a/u/s  (suhWngual 
in  man,  the  rabbit,  dog,  and  cat ;  submaxillary  in  the  dog  and  cat)  ;  (2)  serous 
sa/tTary g/am/s  (the  parotid  in  man,  the  rabbit,  dog,  and  cat;  submaxillary  in 
the  rabbit,  and  the  pancreas) ;  (3)  mixed  salivary  glands  (submaxillary  in  man, 
the  ape,  guinea-pig,  and  mouse). 

The  Sublingual  Gland. — The  excretory 
duct  (duct  of  Bartholin)  consists  of  a  two- 
layered  cylindrical  epithelium  and  fibro-elastic 
tissue.  It  is  continued  as  the  intralobular  or 
mucous  tubes,  whose  low  columnar  epithelium 
exhibits  the  characteristic  striation  only  in  a 
few  places.  Intercalated  tubules  cannot  be 
demonstrated  with  certainty,  and  it  is  much 
more  probable  that  the  mucous  tubes  pass 
directly  into  the  terminal  compartments.  The 
latter  are  com]5osed  of  a  membrana  propria 
and  of  gland-cells.  The  membrana  propria 
is  formed  t)y  stellate  connective-tissue  cells ; 
the  empty  glandular  cells  occur  in  groups,  and 
the  "demilunes"  therefore  appear  very  large. 
The  connective  tissue  between  the  tubules  and 
the  lobules  is  rich  in  leucocytes  (Fig.  146). 

The  Parotid  Gland. — The  excretory  duct 
(duct  of  Stenson)  is  distinguished  by  its  broad, 
compact  membrana  propria  close  beneath  the 
epithelium,  but  is  otherwise  like  that  of  the 
sublingual  gland.     It  divides  and   passes  into 

Xk\t  inlralolmlar  Xwhz?,,  whose  columnar  cells  exliibit  at  the  base  distinct  ver- 
tical striation.  Following  these  are  the  intermediate  tubules,  which  are 
lined  by  elongated,  often  spindle-shaped  cells.  The  intermediate  tubules  con- 
tinue into  the  terminal  compartments,  which  consist  of  a  delicate  mem- 
brana projjria  of  stellate  connective-tissue  cells  and  of  cubical  serous  glandu- 
lar cells.  In  a  condition  of  exhaustion  the  cells  are  small,  dark,  and  granu- 
lar;   in  a  condition  of  activity  they  appear  larger  and  somewhat  lighter. 

The  Submaxillary  Gland. — The  excretory  duct  (duct  of  Wharton)  pos- 
sesses likewise  a  two-layered  columnar  epithelium,  a  connective-tissue  layer 
rich  in  cells,  and  outside  of  this  a  thin  stratum  of  longitudinally-disposed 
muscle-fibers  ;  it  continues  as  the  intralobular  tubes  lined  with  characteristic 
"  rodded  "  epithelium,  which  pass  into  the  short  intermediate  tubules  clothed 
with   cubical   cells.     The   latter  lead  into  the  acini,  which  are  clothed    with 


ic:.  146. —  From  a  Thin  Cuoss-Section 
OF  HumanSublingualGland.  X  240. 
Of  the  seven  tubules  represented,  only 
three  (1,2,3)  are  sectioned  so  as  to  be 
suitable  for  study.  In  2  are  six  cells 
loaded  with  secretion  {s.g) ;  and  two 
empty  cells  (j./)  are  crowded  to  the  peri- 

fhery,  where  they  form  a  "crescent." 
n  3  all  the  cells  are  filled  with  secretion, 
and  have  deeply  slamcd  contents  :  4, 
tangential  section  of  a  similar  tubule. 
5,  6,  7.  Oblique  sections  of  tubules  like 
I  ana  2,  which  show  the  crescents,  but 
not  the  lumen  of  the  gland,  mp.  Mem- 
brana propria.  b.  Connective  tissue 
with   numerous  leucocytes,  z.     Tcchn. 


172 


HISTOLOGY. 


either  serous  gland-cells  (as  in  the  parotid)  or  with  mucous  gland-cells  and 
demilunes. 

The  Pancreas. — The  excretory  duct  (duct  of  Wirsung  and  Santorini)  is 
formed  of  a  simple  columnar  epithelium  and  fibrous  connective  tissue,  which 
latter  is  denser  beneath  the  epithelium,  looser  toward  the  periphery.      The  walls 


Fic.  147.— From  a  ThinSectioi 
OF  Human  Pakotid  Gland 
X  240.  .?.  Intercalated  tiibule 
the  outlines  of  the  cells  canno 
be  distinguished.  The  vcr' 
narrow  lumen  of  the  gland 
tubule  is  seen  only  at  /:  th 
remaining  gland-tubules  are  cu 
obliquely.     Techn.  No.  112. 


•'iG.    148. —  From    a  Thin  Sbction  of  Huivian  SuBtflAJ 
X  240.    A.  Cross-sectionof  salivary  tube:  the  epithelial- 
are  partially  loosened  from  the  surrounding  connect! 
same  side  the  striation  in  the  outer  zone  of  the  cells  i 
of  wandering   leucocytes  ;    j,  secretion.     B.  Tubul 
gland-cells  showing  four  lumina  ;  e,  tubules  with  set 
ing  one  lumen  ;  b,  blood-vessels,  of  which  the  \~ 
dinally  and  contains  colored  blood-corpuscles.     Tech 


>n  the  right 

.  *  :  on  the 

I ;  k,  nuclei 

(m)   with  mucous 

i  gland-cells  show- 

ut  longitu- 

No.  112. 


of  the  main  e.xcretory  duct  and  its  larger  branches  contain  minute  mucous  glands. 
Intralobular  tubes  with  their  characteristic  epithelium  are  wanting.  The 
branches  of  the  excretory  duct  continue  directly  into  the  intermediate  divisions. 
The   columnar  epithelial  cells  of  the   former  steadily  diminish  in  height  and 


B  -£r7^57»^^^(I^^_N_  Terminal   compartment   (tangen- 

,  ^      *  ^ "''  ^c^    \:K.         •   ^         ^'^*  section). 


Intermediate    tubule    (longitudi- 
~     nal  section). 


.  Acinus  (halved). 
Intermediate    tubule    (t 


n). 
-Acinus  (halved). 


Fig.  149.— .-^.  Gland-Cells  of  Pancreas  of  C 
below,  two  isolated  cells.    B.  From  a  Cross-Se 


irmediate  tubule. 

X  560.     Above,  groups  of  cells  as  they  usually  appear; 
N  op  Pancreas  of  AN  Infant.   X  240.    Techn.  No.  113. 


eventually  pass  over  into  the  flattened  cells,  placed  parallel  to  the  long  axis,  of 
the  intermediate  tubules.  These  tubules  are  very  long  and  narrow ;  toward 
the  acini  they  divide  and  then  terminate  abruptly. 

The  epithelium  of  the  acini  is  composed  of  short  cylindrical  or  conical 
cells,  which  are  characterized  by  the  highly  refracting   granules — "zymogen 


THE    DIGESTIVE    OROANS. 


173 


granules  " — occupying  the  zone  adjoining  the  lumen,  and  are  thus  distinguished 
from  all  other  glandular  cells  (Fig.  149  A).  The  clearer  peripheral  zone  con- 
tains the  round  nucleus.  The  granular  and  clear  divisions  of  the  cell  vary  in 
proportionate  extent  with  the  functional  condition  of  the  cell.  In  the  beginning 
of  digestion  the  granules  disappear  and  the  clear  belt  becomes  deeper.  Sub- 
sequently the  granular  zone  increases  to  such  an  extent  that  it  occupies 
nearly  the  whole  of  the  cell.  In  a  fasting  condition  the  two  zones  are  of 
equal  size. 

In  glands  treated  by  the  method  of  Golgi,  the  secretion  often  stains  and 
the  duct-system  in  its  entire  extent  appears  black.  It  may  then  be  seen  that 
strife  radiate  out  from  the  central  lumen,  but  do  not  quite  extend  to  the 
membrana  propria  ;  they  branch,  and  without  anastomosing  terminate  in  free 
ends.  They  must  not,  without  further  consideration,  be  compared  with  the 
secretory  capillaries  of  the  parietal-cells,  for  these  form  a  network  embracing 
the  cell,  while  here,  at  the  most,  the  stria;,  not  their  branches,  lie  upon  the 
gland-cells  ;  the  latter  lie  rather  within  the  cell  and,  in  my  opinion,  indicate 
the  residue  of  elaborated  secretion  that  remains  in  the  otherwise  empty  cell 
(also  in  the  submaxillary,  in  the  "demilunes").      (Fig.  150  and  Fig.  151.) 


X  320.    Techn.  No.  119. 


-From  a  Section  t 
OF  Dog.     X  3=o.    ' 


The  blood-vessels  of  the  salivary  glands  are  richly  developed.  The  arterial 
stems  run,  as  a  rule,  along  the  main  excretory  duct,_  divide  into  numerous 
branches  which  pass  between  the  lobules  and  finally  penetrate  within  the  latter, 
where  they  break  up  into  capillaries  and  form  close  networks  embracing  the 
tubules.  The  capillaries  lie  in  immediate  proximity  to  the  gland-cells.  The 
larger  veins  follow  the  course  of  the  arteries. 

With  regard  to  the  lymph-vessels  little  is  known  with  certainty.  The 
interfascicular  clefts  between  the  lobules  and  the  tubules  have  been  described  as 
lymph-channels. 

The  salivary  glands  are  profusely  supjjlied  with  meduUated  and  nonmedul- 
lated  nerves,  along  the  courseof  which  microscopic  groupsof  ganglion-cells  occur. 
The  fine  meduUated  nerve-fibers  form  networks  around  the  gland-tubules,  but 
do  not  penetrate  them,  and  ramify  in  the  walls  of  the  blood-vessels. 


174 


HISTOLOGY. 


THE  LIVER. 
The  liver  is  a  compound  tubular  gland.  On  making  an  incision  into  a 
liver  or  on  examining  its  outer  surface,  it  will  be  observed  that  it  is  divided 
into  irregular  polygonal  areas,  well  defined,  as  in  the  hog,  or  poorly  defined, 
as  in  man  and  the  majority  of  mammals.  These  areas  are  the  lobules  of  the 
liver  (incorrectly  named  acini).  Their  real  form  is  somewhat  like  that  of  a 
prism  with  a  rounded  upper  end  and  a  transversely-blunted  base  (Fig.  152). 
They  are  2  mm.  high  and  i  mm.  broad.  Close  under  the  capsule  of  the  liver 
the  lobules  are  often  arranged  with  their  apices  looking  toward  the  surface,  and 
a  section  taken  parallel  to  the  surface  will  pass  through  the  lobules  transversely 
(Fig.  154)  ;  in  the  interior  of  the  liver  the  lobules  extend  in  different  direc- 
tions. Each  lobule  consists  of  gland- 
cells  and  blood-vessels  and  is  separated 
from  neighboring  lobules  by  the  inter- 
lobular connective  tissue — the  capsule  of 
Glisson — which  supi)orts  the  branches  of 
the  excretory  duct — the  hepatic  duct — 
the  branches  of  the  portal  vein  and  the 
hepatic  artery,  the  lymph-vessels  and  the 
nerves.  The  demarcation  of  the  lobules 
depends  on  the  development  of  the  inter- 
^_  ,  lobular  connective  tissue. 

|^,^<~»->        ^  The  main  excretory  duct,  the //c/(7//f 

duct,  and  its  larger  branches  are  com- 
posed of  a  single  stratum  of  columnar 
epithelium,  occasionally  containing  gob- 
let-cells, and  of  fibrous  connective  tissue 
separated  into  a  tunica  propria  and  sub- 
mucosa.  The  tunica  propria  contains 
glands,  chiefly  short  pear-shaped  follicles 
lined  with  mucous  gland-cells,  and  also 
isolated  longitudinally- and  transversely-disposed  plain  muscle-fibers. 

The  cystic  duct,  the  ductus  choledochus,  and  the  gall-bladder  exhibit  the 
same  structure  ;  the  tunica  propria  is  elevated  into  minute  anastomosing  ruga;, 
and  the  mucosa  is  supplemented  by  a  thin  layer  of  smooth  interlacing  muscle- 
fibers.  The  columnar  epithelial  cells  of  the  gall-bladder  are  distinguished  by 
their  height  (0.05  mm.)  from  those  of  the  ductus  choledochus  (0.024  mm.). 
The  vasa  aherrantia  or  blind  bile-ducts,  that  occur  chiefly  at  the  left  border 
of  the  liver,  at  the  portal  fissure,  and  surrounding  the  vena  cava,  are  em- 
bryonal remains  of  liver-substance  (isolated  bile-ducts)  and  do  not  occur  in 
the  parenchyma  of  the  organ.  The  branches  of  the  hepatic  duct — inter- 
lobular bile-ducts — exhibit  thinner  walls  as  they  diminish  in  caliber ;  the  larger 
are  composed  of  simple  columnar  epithelium  and  fibro-elastic  tissue  ;  the  small- 


HEME  OF  A  Hepatic  Lobuli 
I  tninsverse  section  below  an 
partial  leveling,  in  longitudinal  section  : 
In  the  left  half  the  blood-vessels  are  drav 
the   right  half  only  the  cords  of  hepatic 


d,   by 


THE    DIGESTIVE    ORGANS. 


175 


est  possess  only  a  structureless  membrana  propria  and  a  simple  layer  of  low 
epithelial  cells,  often  showing  a  cuticular  border,  which  as  they  enter  at  the 
margin  of  the  lobules  annex  themselves  directly  to  the  true  glandular  cells. 
This  transition  is  very  difficult  to  see,  and  can  only  be  distinctly  perceived  in 
sections  in  which  the  bile-ducts  have  been  injected  or  blackened  by  Golgi's 
silver  method. 


Fig.  153. — Livbr-Cells  op  Man.     X  560.     A.  Isolated  liver-cells  containing  smaller  and  larger  fat-drops,/"; 

b,  impression  resulting  from  a  blood-vessel.    Techn.  No.  114. 

B.  I'rom  a  section  ;  i .   Exhausted  cells ;  2,  active  cells,  filled  with  secretion.     Techn.  No.  116. 

The  glandular-cells  of  the  liver,  the  hepatic  cells,  are  irregular  polyhedral 
elements  consisting  of  a  granular  protoplasm  and  of  one  or  more  nuclei  ;  they 
have  no  cell-membrane.  The  protojilasm  contains  granules  of  pigment  and 
globules  of  fat  of  various  sizes.      The  cells  vary  in  size  from  i8  to  26  ,a.      The 


■< 


'\        *''      '    ,'    *    ~      ".!    '         'y      •      p"^'.         ^Interlobular  bile-duct. 
;-■■->•'.•;".■•.•"-•'■'..      /    ",'■,'•  •■''VI' ^•''- .  Interlobular 


^^^^|;:v:-'!;v: 


I 


■-■■  '■^:^'% 

'■  ''i^ir-^ 

Fic.  154— From  a  Horizontal  Section  i>i    l^•,l^N  Iivik.  ^■,      I  l.n.- ciitial  veins,  cut  transversely, 

represent  each  a  center  of  as  many  hepatic  lobules,  which  at  the  periphery  are  but  slightly  defined  from  their 
neighbors.  Helow  and  to  the  right  of  the  section  the  lobules  are  cut  obliquely  and  their  boundaries  cannot  be 
distinguished.    I'echn.  No.  116. 


appearance  of  the  hepatic  cells  depends,  as  in  other  glands,  on  the  phase  of 
functional  activity.  In  a  fasting  condition  they  are  small  and  dark,  and  have 
indistinct  contours  ;  during  digestion  they  are  larger,  have  a  clear  center,  and 
at  the  periphery  a  coarsely-granular  zone.  In  man  the  two  conditions  are 
frequently  e.xhibited  in  the  same  liver  (Fig.  153  B). 


176 


HISTOLOGY. 


In  the  lower  vertebrates  (amphibians  and  reptiles)  the  hepatic  cells  form 
typical  tubes,  but  in  the  higher  vertebrates  their  arrangement  is  a  very  peculiar 
one,  and  not  a  trace  of  tubular  structure  is  to  be  seen,  as  might  be  presupposed 
from  the  tubular  character  of  the  liver.  The  cells  are  united  in  small  trabeculse 
or  cords,  the  so-called  conls  of  cells,  which  are  radially  disposed  around  a 
small  vein  (the  central  vein)  situated  in  the  axis  of  the  lobule,  and  by  lateral 
branches  anastomose  with  neighboring  cords  of  cells.  A  lumen  cannot  be 
distinguished  in  sections  prepared  by  the  usual  methods  ;  it  can  only  be  shown 
by  injecting  the  system  of  canals  from  the  hepatic  duct  or  by  employing  Golgi's 
method,  which   blackens  the  bile.      In  such  preparations  it  may  be  seen  that 


Small    interlobu- 
lar   bile -duel, 

bile-capiUa- 


Boundary,  toward  central  > 


method  of  Golgi. 


the  minutest  interlobular  bile-ducts  are  continued  directly  into  the  lobules, 
where  they  form,  apparently,  a  network  with  polygonal  meshes.  In  reality 
there  are  but  few  true  meshes  ;  the  network  is  simulated  by  the  zigzag  course 
of  the  bile-canaliculi  and  the  crossing  in  different  planes  of  the  blind  lateral 
twigs  with  which  they  are  furnished  (Fig.  155). 

The  ramifications  of  the  intralobular  system  of  canaliculi  appear  to  have 
little  relation  to  the  branching  of  the  cords  of  hepatic  cells.  The  latter  branch 
much  less  than  the  former  and  thus,  apparently,  the  intralobular  canaliculi  have 
attained  a  certain  degree  of  independence,  as  implied  in  the  name  Inle-caftillaries 
bestowed   upon   them.     This  also  accounts   for  the  hitherto   always   fruitless 


THE    DIGESTIVE    ORGANS. 


177 


endeavor  to  demonstrate  a  special  wall  for  the  bile-capillaries.  There  can  be 
no  wall  other  than  that  formed  by  a  modification  of  the  exoplasni  of  that  side 
of  the  hepatic  cells  at  which  the  capillary  is  situated. 

Thin  sections  show  clearly  that  the  bile-capillaries  stand  in  the  same  rela- 
tion to  the  hepatic  cells  as  the  lumina  of  other  glands  do  to  the  surrounding 
gland-cells,  at  least  in  most  cases.  But  nevertheless  certain  differences  exist. 
The  first  difference  is  this,  that  only  a  few,  usually  two,  hepatic  cells  bound  the 
bile-capillaries,  while  in  other  glands  the  lumen  is  surrounded  by  several  cells. 
The  explanation  of  this  may  be  found  in  the  conspicuous  difference  between  the 
diameter  of  the  lumen  (bile-capillary)  and  that  of  the  hepatic  cell ;  two  cells  are 
sufficient  to  completely  surround  the  lumen.  The  capillary  is  thus  formed  by  the 
apposed  furrow-like  depressions  of  two  contiguous  hepatic  cells  (Fig.  162). 
A  second  difference  consists  in  the  relation  of  the  surfaces  of  the  hepatic  cells 
to  the  bile-capillaries  ;  they  are  in  contact  with  the  bile-capillaries  not  only  on 
one,  but  on  several  surfaces.  This  momentarily  confusing  fact,  though  not  a 
frequent,  is  nevertheless  not  an  isolated  phenomenon.  One  need  but  recall 
the  relations  in  the  fundus  glands, 
where  lateral  twigs  leave  the  chief 
lumen,  branch  and  form  a  complete 
basket-work  of  fine  canals  embrac- 
ing the  parietal-cells,  and  where 
each  parietal-cell  presents  not  only 
one  but  all  surfaces  to  the  gland- 
lumen  ;  but  there  the  phenomenon 
is  not  so  striking,  because  the 
branching  off  of  the  small  lateral 
canals  from  the  main  lumen  is  easily 
recognized  ;   in  the  liver  the  lateral 

branches  of  the  bile-cajjillaries  are  of  the  same  diameter  as  the  main  lumen  and 
are  often  of  considerable  length,  subdivide,  and  may  even  anastomose  directly 
with  neighboring  bile-capillaries,  although  this  does  not  commonly  occur,  and 
thus  every  possibility  of  distinguishing  between  bile-capillaries,  main  lumen, 
and  lateral  canals  vanishes.  The  fact  tiiat  the  hepatic  cells  are  in  contact  with 
the  bile-capillaries  not  only  on  one  but  on  several  surfaces,  renders  compre- 
hensible the  luxuriant  ramification  of  the  latter,  despite  the  fact  that  few  cells 
are  required  to  circumscribe  them. 

Not  infrequently  it  may  be  seen  that  short  fine  lateral  twigs  leave  the  bile- 
capillaries  and  terminate  in  a  minute  knob-shaped  end.  The  knob  corresponds 
to  a  small  vacuole  in  the  liver-cell,  which  communicates  with  the  bile-capillary 
by  means  of  the  minute  lateral  twig.  These  are  undoubtedly  transient  forma- 
tions occurring  in  connection  with  certain  functional  phases;  the  proof  of  this 
I  detect  therein  that  entire  areas  of  the  system  of  canaliculi  may  be  free  from 
these  knobs,  while  close  beside  every  capillary  is  beset  with  them  (Fig.  156). 

Of  the  blood-vessels  of  the  liver,  the  portal  vein  assumes  the  role  that  falls 
to  the  artery  in  other  glands,  while  the  hepatic  artery  is  assigned  the  subordi- 


178 


HISTOLOGY. 


nate  part  of  the  maintenance  of  the  interlobular  branches  of  the  bile-ducts,  of 
the  portal  vein,  and  of  the  nerves. 

From  the  branches  of  the  portal  vein,  which  because  they  run  in  the  inter- 
lobular connective  tissue  are  called  interlobular  veins,  spring  numerous  capil- 
laries, possessing  a  width  of  lo  to  14  //.  They  penetrate  within  the  lobules, 
anastomose  repeatedly  during  their  course,  and  finally  empty  into  a  small  vein 
lying  in  the  axis  of  the  lobule,  the  central  {intralobular')  vein  visible  in  trans- 
verse and  longitudinal  sections  even  in  the  uninjected  liver  (Fig.  154).  The 
central  veins  represent  the  radicles  of  the  hepatic  veins  and  empty  into  the 
sublobular  veins,  which  run  along  the  slightly-flattened  side,  the  so-called  base, 
of  the  hepatic  lobules  (Fig.  159). 


nterlobulares. 
Vense  intralobuldres  (i  entral). 


'iG.  157.— Horizontal  Section  of  Liver  of  Rab- 
bit. Injected  through  the  portal  vein.  X  40. 
Three  hepatic  lobules  are  represented.  The  injec- 
tion mass  filled  only  the  branches  of  the  portal  vein 
(interlobular  veins) ;  in  the  upper  lobule  it  penetrated 
to  the  central  vein.     Techn.  No.  118. 


Fig.  158. — Horizontal  Section  of  Liver  of 
Injected  through  vena  cava  inferior.  X  40- 
iiepatic  lobules  are  shown.  The  injection  masj 
the  central  vein  and  the  capillaries  emptying  i 
l)ut  did  not  penetrate  to  the  interlobular 
Techn.  No.  1.8. 


The  relations  between  the  portal  capillaries  on  the  one  side  and  the  he- 
patic cells  and  bile-capillaries  on  the  other  calls  for  especial  consideration. 
Between  the  meshes  of  the  portal-capillary  network  lie  the  cords  of  hepatic 
cells,  and  the  relation  of  the  blood-vessels  and  gland-cells  is  consequently  a 
very  intimate  one  ;  sections  show  that  a  hepatic  cell  is  in  contact  with  capillar- 
ies, not  only  on  one  but  on  several  sides  (Fig.  i6o).  This  is  a  peculiar  phe- 
nomenon ;  it  does  not  occur  in  other  glands,  in  which  the  blood-vessels  touch 
the  cells  only  at  one  surface,  and  is  only  comprehensible  when  we  recall  that 
in  cross-sections  the  lumen  (bile-capillary)  is  bounded  by  two  cells,  while  in 
other  glands  the  lumen  is  bounded  by  six  or  more  cells  (Fig.  i6i).  But  as  in 
other  glands,  so  also  in  the  liver,  the  cells  are  inserted  between  the  lumen  on 


THE    DIGESTIVE    ORGANS. 


179 


the  one  hand  and  the  blood  vessels  on  the  other.  Nowhere  do  blood-capil- 
laries and  bile-capillaries  lie  close  beside  one  another;  they  are  always 
separated  by  an  intervening  portion  of  the  cell.  The  most  convincing 
demonstration  of  this  is  afforded  bv  thin  sections  of  rabbit's  liver,  in  which 


Central  (intralobular) 


''*iA. 


Fig.  159. — Fhom  a  Vertical  Section  op  Liveu  op 
vein  cut  longitudinally  ;  it  takes  up  the  central  vci 
the  wide  blood-vessels.     X  iS-    Techn.  No.  118. 


r.     Injection  through  vena  cava 
The  greater  part  of  the  injecti( 


the  blood-vessels  have  been  cut  transversely ;  these  show  plainly  that  the  bile- 
capillaries  run  along  the  surfaces,  the  vascular  capillaries  at  the  corners  of  the 
hepatic  cells  (Fig.  162);  however,   this  is  not  invariably  the  case;   the  bile- 


i,  i6o.^From  a  Section  op  Livek  of  Rabbit.  X  340.  The  portal-capillaries  were  injected  w 
mass,  the  bile-capillaries  with  a  blue  mass.  The  hepatic  cells  are  in  contact  with  the  blood-capillarie 
sides.  At  a  few  points  the  red  mass  has  retracted  and  given  rise  to  a  space  (/),  between  the  hepatic 
portal-capillaries.  The  bile-capillaries  are  nowhere  in  contact  with  portal-capillaries  but  arc  alwa 
rated  from  them  by  half  the  breadth  of  a  cell.  The  dark  spots  on  the  portal-capillaries  are  optit 
sections  of  blood-capillaries  which  run  vertically  to  the  plane  of  the  section. 


capillaries  sometimes  run  along  the  edges,  a  disposition   that  occurs  e.specially 
in  man  (Fig.  162  X). 

The  branches  of  the  hepatic  artery  follow  the  course  of  the  portal  vein 
and  ramify  only  in  the  interlobular  tissue  ;  they  form  capillary  networks  about 


i8o 


HISTOLOGY. 


the  larger  bile-ducts,  the  branches  of  the  portal  and  the  hepatic  veins.  These 
capillaries  are  taken  up  by  the  portal  interlobular  veins  or  by  the  portal  capil- 
laries at  the  margin  of  the  lobules.  In  the  capsule  of  the  liver  the  hepatic 
artery  forms  a  wide-meshed  capillary  plexus.      The  course  of  the  blood-vessels 


Gland-lumen  (bile-capil- 
lary). 


ll,R,. 


is  therefore  as  follows:  The  portal  vein  enters  at  the  transverse  fissure,  divides 
repeatedly  into  branches  that  steadily  decrease  in  size  and  run  in  the  connective 
tissue  between  the  lobules  as  the  interlobular  veins  ;  these  break  up  into  capilla- 
ries which  pass  toward  the  axis  of  the  lobule  and  terminate  in  the  central  vein. 


Flu.  162. — Thin  Section-  of  Liver  of  R 
nut  schematic.)  Two  of  the  hepatic 
capillary  at  the  edge  of  a  hepatic  cell. 


Injected  Bile-Capillaries.    X  560.    (The  t 
contact  with  four  blood-capillanes  (i,  2,  3,  4). 


Several  of  the  latter' unite  in  the  formation  of  each  of  the  sublobular  veins, 
which,  like  the  larger  hepatic  veins  they  form  by  their  union,  run  between  the 
lobules. 

The  capsule  of  the  liver  is  composed  of  fibre-elastic  tissue,  which  is  espe- 
cially well  developed  at  the  transverse  fissure,  where  it  is  called  the  capsule  of 


THE    DIGESTIVE   ORGANS. 


l8l 


^W^ 


[G  163. — From  a  Shake 
Human  Livek.  X  240.  c.  Blood- 
capillaries,  at  X  still  containing  blood- 
corpuscles,  d.  Interlobular  connective 
tissue.  On  the  right  are  five  hepatic 
cells :  the  others  nave  fallen  out  of 
the  meshes  of  the  capillary  network. 
I'echn.  No.  117. 


Glisson,  and  in  the  form  of  special  sheaths  for  the  different  channels  penetrates 
the  interior  of  the  liver,  where  it  is  usually  found  in  such  small  amounts  between 
the  lobules  that  the  boundaries  of  the  latter  are  very  imperfectly  defined.  The 
walls  of  the  veins  are  firmly  attached  to  the  liver  substance  by  the  interlobular 
connective  tissue,  and  for  this  reason  do  not 
collapse  when  cut.  Delicate  fibers  ("  lattice- 
fibers")  derived  from  the  interlobular  connec- 
tive tissue  penetrate  into  the  interior  of  the 
lobule,  where  they  are  arranged  in  the  form  of 
a  delicate,  radially-placed  "latticework." 

The  lymph-vessels  accompany  the  branches 
of  the  portal  vein,  which  they  embrace  in  their 
ramifications;  with  the  portal  capillaries  they 
enter  the  interior  of  the  hepatic  lobules,  ac- 
company them  close  up  to  the  central  vein, 
then  pursue  a  divergent  course.  The  deep 
lymphatics  communicate  with  a  superficial  net- 
work of  lymph-vessels,  which  occur  in  the 
capsule. 

The  nerves  consist  largely  of  nonmcdul- 
lated  fibers  with  which  a  few  meduUated  nerve- 
fibers  are  mingled;  they  enter  the  interior  of  the  liver  in  company  with  the 
hepatic  artery  and  follow  its  ramifications ;  the  exact  mode  of  their  termination 
is  unknown.     Ganglion-cells  occur  along  the  course  of  the  nerves. 

The  secretion  of  the  liver,  the  bile, 
frequently  contains  drops  of  fat,  also  granu- 
lar masses  of  bile-pigment.  Columnar  cells 
from  the  bile-ducts  are  incidental  admix- 
tures. 

That  the  structure  of  the  liver  really 
follows  the  type  of  the  tubular  glands,  and 
that  the  cords  of  hepatic  cells,  with  certain 
modifications,  are  comparable  to  the  acini 
of  other  glands,  the  foregoing  considerations 
have  shown.  The  hepatic  lobules,  on  the 
other  hand,  cannot  without  explanation  be 
compared  with  the  lobules  of  other  glands ; 
the  latter,  as  a  rule,  consist  of  a  duct-system, 
of  which  the  excretory  duct  leaves  the  lobule 
at  one  place  and  continues  into  a  larger  duct. 
In  the  hepatic  lobules  the  ducts  emerge  at 
many  points  on  the  surface.  'I'he  acconijianying  schematic  representations  may 
serve  to  elucidate  the  relations  of  the  lobules.  Imagine  a  system  of  ducts  ;  along- 
side the  excretory  duct  an  artery,  whose  capillaries  surround  the  terminal  com- 
partments and  i)ass  into  a  vein  running  along  the  base  of  the  latter  (Fig.  164). 


Excretory  duct 


compartments 
F   A  System  of    Ex 

("  DUCT-SVSTEM  "). 


HISTOLOGY. 
Excretory  ducts.  Branch  of  portal  > 


Terminal  comparti 

Fig.  165. — Scheme  of  the  Liver.     Two  lobules  areshown,  of  which  the  left  is  only  half  carried 

of  the  capillaries  and  the  cords  of  hepatic  cells  have  been  omitted  for  the  sake'of 


Branch  of  portal 


Fig.  166. — Scheme  of  Transverse  Section  of  Liver.     Four  lobules  represented.    The  separate  systems  ol 
ducts  are  indicated  by  the  difference  in  shading,     A.   Excretory  ducts.    £.  Terminal  compartments. 


THE    DIGESTIVE    ORGANS. 


183 


This  is  the  principle  of  each  of  the  many  systems  of  ducts  of  which  the  liver  con- 
sists ;  but  there  is  one  peculiarity  :  the  somewhat  tortuous  terminal  compartments 
extend  in  certain  different  directions  (Fig.  165).  At  the  base  as  well  as  above 
runs  a  vein,  but — another  variation — the  vein  takes  up  not  only  these  capillaries 
but  also  those  of  the  other  side,  where  lies  another  system  of  ducts  whose  acini 
are  in  contact  at  the  base  with  the  same  vein.  The  vein,  therefore,  lies  in  the 
axis  of  a  complex  or  aggregation  of  terminal  compartments,  and  such  a  complex 
is  termed  an  hepatic  lobule.  (In  the  liver  of  the  rabbit  the  central  veins  lie 
close  under  the  surface,  and  only  take  up  capillaries  from  one  side. )  If  we  now 
draw  a  comparison  with  the  scheme  Fig.  164,  the  artery  corresponds  to  the 
portal  vein  in  scheme  Fig.  165,  and  the  vein  in  Fig.  164  is  the  equivalent  of  the 
central  vein  of  Fig.  165  ;  one  hepatic  lobule  corresponds  not  to  one  duct- 
system,   but    to   parts  of  several  systems.     The  simijlicity  of  this   schematic 


Grratbr  Omentum  of  Ti/t 
ve  tissue.     The  wavy  striatic 

IS  mounted  in  damar.     At   X   lb 

hn.  No.  120. 


BIT.  X  240.  The  network  is  formed  by  large  and  small 
of  the  bundles  can  only  be  indistinctly  seen,  because  the 
cells  from  the  opposite  surface  can  be  seen  shimmering 


presentation  is  based  in  part  on  the  conception  of  well-defined  lobules,  as  they 
occur  in  the  hog.  In  other  animals  the  distribution  of  the  terminal  ramifi- 
cations is  less  regular;  the  latter  bend  into  neighboring  lobules,  to  which  in 
part  is  owing  their  less  distinct  demarcation.  Each  system  of  ducts  partici- 
pates in  the  formation  of  several  lobules. 


THE  PERITONEUM. 

The  i)eritoneum  consists  principally  of  bundles  of  fibrous  connective  tissue 
and  numerous  elastic  networks ;  the  free  surface  is  covered  by  a  simple  layer 
of  flat  polygonal  epithelial  (endothelial)  cells.  The  connection  with  subjacent 
parts  (the  parietes,  the  viscera,  etc.)  is  effected  by  loose  (subserous)  connec- 
tive tissue. 

The  connective-tissue  bundles  are  arranged  in  thinner  (in  the  visceral 
lieritoneum)   or  thicker   (in  the  parietal  peritoneum,  in  the  mesentery)  layers 


184  HISTOLOGY. 

parallel  to  the  surface,  and  interlace  in  various  directions ;  in  certain  localities 
(in  the  greater  omentum,  in  the  middle  of  the  lesser  omentum)  the  bundles 
form  a  beautiful  network  with  polygonal  or  rectangular  meshes.  The  strands 
of  the  network  are  covered  by  plate-like  epithelial  cells  (Fig.  167). 

The  number  of  connective-tissue  cells  among  the  fibrous  bundles  is  on  the 
whole  not  large;  only  in  young  animals  are  larger  groups  of  cells  found; 
they  resemble  plasma-cells  and  probably  bear  a  close  relation  to  the  formation 
of  blood-vessels. 

The  elastic  fibers  in  the  deeper  layers  of  the  peritoneum,  particularly  in 
the  parietal  portion,  are  profuse  and  vigorously  developed. 

The  subserous  tissue  consists  of  loose  connective  tissue,  many  elastic  fibers, 
and  fat  varying  greatly  in  quantity ;  it  is  plentiful  where  the  peritoneum  is 
easily  shifted  over  the  underlying  parts,  but  on  the  liver  and  the  intestine  it  is 
so  much  reduced  that  it  cannot  be  demonstrated  as  a  special  layer.  At  certain 
places,  e.g.,  in  the  broad  ligaments,  numerous  bands  of  smooth  muscle-fibers 
are  found. 

Blood-vessels  and  nen'es  are  scantily  represented  ;  the  latter  terminate  in 
part  in  Pacinian  corpuscles. 

Lymph-vessels  occur  in  the  superficial  and  the  deeper  layers  of  the  peri- 
toneum. 


VI.  THE  RESPIRATORY  ORGANS. 

THE  LARYNX. 

The  mucous  vtembmiie  of  the  larynx  is  a  continuation  of  the  pharyngeal 
mucous  membrane  and  like  this  is  composed  of  an  epithelium,  a  tunica  propria, 
and  a  submucosa  which  binds  the  mucous  membrane  with  underlying  parts.  The 
mucous  membrane  over  nearly  the  whole  of  the  organ  is  covered  by  a  stratified 
ciliated  columnar  epithelium ;  the  ciliary  wave  is  directed  toward  the  cavity  of 
the  pharynx.  On  the  true  vocal  cords,  on  the  anterior  surfaces  of  the  arytenoid 
cartilages  and  on  the  posterior  surface  of  the  epiglottis  the  epithelium  is  of  the 
stratified  scaly  variety.  The  tunica  propria  consists  of  numerous  elastic  fibers 
and  of  white  fibrous  connective  tissue,  which  in  the  lower  animals  is  con- 
densed to  a  membrana  propria  immediately  beneath  the  epithelium.  The 
tunica  propria  is  the  site  of  a  varying  number  of  leucocytes  ;  in  dogs  and 
cats,  solitary  nodules  are  found  in  the  mucous  membrane  of  the  ventricle  of 
Morgagni.  Papillae  occur  mainly  in  the  mucous  membrane  clothed  with  strati- 
fied squamous  epithelium.  The  submucosa  contains  branched  tubular  mucous 
glands  from  0.2  to  i  mm.  in  size. 

The  cartilages  of  the  larynx  are  principally  of  the  hyaline  variety,  which 
in  a  measure  exhibit  the  peculiarities  of  the  costal  cartilages ;  to  this  belong 
the  thyroid,  the  cricoid,  the  greater  portion  of  the  arytenoid  and  often  the 


THE    RESPIRATORY    ORCANS.  1 85 

triticeous  cartilages.  The  epiglottis,  the  cartilages  of  Wrisberg  and  Santorini, 
the  median  portion  of  the  thyroid,  and  the  apex  and  vocal  process  of  the 
arytenoid  cartilages  are  of  the  yellow  elastic  variety.  Occasionally  the  tritice- 
ous cartilages  are  composed  of  white  fibro-cartilage.  Between  the  twentieth 
and  thirtieth  years  of  life  ossification  (chiefly  endochondral)  begins  in  the 
thyroid  and  the  cricoid  cartilages. 

The  larynx  is  richly  supplied  with  blood-vessels  and  nen'es.  The  blood- 
vessels form  two  or  three  networks  in  planes  i>arallel  to  the  surface,  and  a  close 
subepithelial  capillary  plexus. 

The  lymph-vessels  also  form  two  communicating  networks  in  horizontal 
planes,  of  which  the  superficial  has  the  narrower  channels  and  lies  beneath  the 
vascular  capillary  network. 

The  nerves  in  their  course  include  microscopic  ganglia.  In  ])art  they 
terminate  in  end-bulbs  and  taste-buds.  The  latter  are  found  on  the  posterior 
surface  of  the  epiglottis. 

THE  TR.\CHE.\. 

The  ciliated  mucous  membrane  of  the  trachea  possesses  a  structure  like  that 
in  the  larynx,  excepting  that  the  elastic  fibers  form  a  close  network  in  which 
the  fibers  pursuing  a  longitudinal  direction  predominate.  This  network  lies 
immediately  beneath  the  epithelium  and  above  the  glands.  The  cartilages  are 
of  the  hyaline  variety.  The  ])osterior  wall  of  the  trachea  is  composed  of  a 
layer  of  transversely-arranged  jjlain  muscle-fibers,  which  is  usually  covered  by  a 
stratum  of  fibers  extending  longitudinally.  The  mucous  glands  of  the  poste- 
rior wall  are  distinguished  by  their  size  (2  mm.);  they  not  infrequently 
penetrate  the  muscular  layer,  and  lie  in  part  in  the  fibrous  tissue  behind  it. 

The  behavior  of  the  blood-vessels,  lymph-vessels,  and  nerves  is  the  same 
as  in  the  larynx. 

THE  BRONCHI  .\ND  THE  LUNGS. 

Tile  lungs  may  be  regarded  as  compound  alveolar  glands,  in  which,  as 
in  all  glands,  excretory  and  secretory  (in  this  case  respiratory)  portions  may 
be  distinguished.  The  excretory  division  comprises  the  larynx,  the  trachea, 
and  the  bronchi.  Each  bronchus  on  entering  the  lung  divides  repeatedly  and 
within  the  same  undergoes  continual  subdivision,  giving  off  small  lateral 
twigs  and  branching  at  acute  angles,  with  gradual  decrease  in  the  caliber  of 
the  branches,  finally  breaking  up  into  minute  twigs  that  now'here  anastomose 
with  one  another  and  that  retain  the  characteristics  of  the  bronchus  to  a 
diameter  of  0.5  mm. 

At  this  point  the  respiratory  division  begins.  Isolated  hemispherical 
evaginations,  the  alveoli,  appear  at  irregular  intervals  on  the  walls  of  the  minute 
bronchi.  Such  bronchi  are  called  respiratory  or  terminal  bronchioles.  These 
divide  and  lead  into  the  alveolar  ducts,  which  differ  from  the  terminal  bron- 
chioles only  in  the  larger  number  of  alveoli  in  their  walls.  The  alveolar 
ducts  divide  at  right  or  acute  angles,  and  pass  without  sharp  demarcation  into 


1 86  HISTOLOGY. 

the  slightly-expanded  terminal  vesicles  (less  correctly,  infundibula),  whose  walls 
are  thickly  beset  with  alveoli. 

The  entire  respiratory  division  is  separated  by  areolar  tissue  into  lobules 
0.3  to  3  cm.  in  size.  All  the  branches  of  the  excretory  division  to  a  diameter 
of  1.5  to  I  mm.  and  less  lie  between  the  lobules — as  "interlobular  ducts." 

The  minute  structure  of  the  bronchi  in  the  largest  branches  does  not  differ 
from  that  of  the  trachea.  Gradually,  however,  modifications  appear,  which 
first  involve  the  cartilages  and  the  musculature.     The  C-shaped  ring  cartilages 


Fig.  i63.— Ckoss-Se 


Two  MiLLiMETEKS  Thick,  OF  Child.     X  30-     Techii.  No.  123. 


are  replaced  by  irregular  plates  lying  on  all  sides  of  the  bronchial  wall.  They 
diminish  in  size  and  thickness  with  the  decrease  in  the  diameter  of  the  bronchi 
and  disappear  altogether  in  bronchioles  1  mm.  in  diameter. 

The  smooth  muscle-fibers  are  circularly  disposed  in  a  continuous  layer 
lying  within  the  cartilages  and  form  a  complete  investment  for  the  tube. 
The  thickness  of  the  muscular  layer  decreases  with  the  diameter  of  the 
bronchi  ;  but  muscle-fibers  are  still  found  as  far  as  the  alveolar  ducts.  In  the 
infundibula  thev  are  wanting. 


IHE    RESPIRATORY    ORGANS. 


■  87 


The  miiioiis  iiiemliranc  is  thrown  into  longitudinal  folds  and  consists  of 
a  stratified  ciliated  epithelium  containing  goblet-cells,  which  in  the  smaller 
bronchi  becomes  gradually  reduced  to  a  single  stratum,  and  of  a  connective- 
tissue  tunica  pro[)ria.      The  latter  contains  numerous  longitudinal  networks  of 


Fig.  169.— From  a  Section  of  Lung  of  Adult  Man.  X  50.  The  terminal  bronchiole  divides  into  two 
branches  (on  the  right).  A  portion  of  the  wall  of  the  bronchiole  fell  within  the  plane  of  the  section.  Above 
the  entrance  to  the  alveoli  can  be  seen  ;  below  the  alveoli  are  viewed  from  the  side.  The  epithelium  of  the 
V. ..k:..!.  ;^  "'=xed.     The  epithelial  lining  of  the  alveoli  is  only  partially  visible  with  this  magnification. 


the  entr^.- 
__  ichiole 
Techn.  No.  1 


elastic  fibers  and  leucocytes  in  greatly  varying  numbers.  Occasionally  solitary 
nodules  occur,  from  the  crest  of  which  leucocyte*  wander  through  the  epithe- 
lium into  the  bronchial  tubes. 


Cnbical  and  flat  epithelial  cells. 


Fig.  170- — From  Sections  op  Human  Ll'ng  (.\  and  B),  and  fC),  op  Lung  op  t 
X  540  A.  Mixed  epithelium  of  terminal  bronchiole.  B  and  C.  Alveoli  drawn 
margin  of  the  alveolus  is  shaded  ;  it  can  he  seen  that  the  epithelium  covering  it  i 
alveolus  (the  light  portion)  ;  the  nuclei  of  the  cells  are  not  visible.     Techn.  No. 


Kitten  Nine  Days  Old. 
with  change  of  focus.  The 
like  that  in  the  base  of  the 


Branched  tubular  mucous  glands  occur  as  far  as  the  cartilages  extend  ; 
they  are  situated  outside  of  the  muscular  layer  (Fig.  i68).  They  are  numer- 
ous and  do  not  disappear  until  at  the  beginning  of  the  respiratory  bronchioles. 

F.xternal  to  the  cartilages  is  z^fibro-elastic  tunic  which  envelops  the  entire 
bronchus  including  the  accompanying  vessels  and  nerves. 


iSa  /  HISTOLOGY. 

The  minute  structure  of  tlie  respiratory  division,  after  the  gradual  disap- 
pearance of  the  cartilages  and  glands,  is  distinguished  especially  by  the  nature 
of  the  epithelium. 

The  respiratory  bronchioles  following  the  smallest  excretory  bronchi  still 
contain  a  single  layer  of  ciliated  columnar  epithelium,  but  as  they  proceed  the 
cilia  are  lost,  the  cells  become  cubical,  and  between  these  another  kind  of 
epithelial  cells  appears,  in  the  form  of  thin  nonnucleated  plates  of  different 
sizes.  These  plates  and  isolated  or  small  groups  of  cubical  cells  form  an  epi- 
thelium called  respiratory  epithelium.  The  transition  of  the  cubical  into  the 
respiratory  epithelium  is  not  abrupt  and  sharply  defined,  but  occurs  in  such 
wise  that  at  one  extremity  of  the  bronchiole  cubical,  at  the  other  extremity 
respiratory  epithelium  is  found  ;  or  that  groups  of  cubical  cells  are  surrounded 
by  respiratory  epithelium  or  the  reverse.  The  respiratory  bronchioles  contain, 
therefore,  a  mixed  epithelium  (Fig.  169  and  Fig.  i']oA). 

The  epithelium  of  the  alveolar  ducts  and  of  the  alveoli  is  the  same  as  the 
respiratory  epithelium  of  the  bronchioles.  The  developmental  history^teaches 
that  the  smaller  nonnucleated  plates  originate  from  cubical  cells  which 
become  flattened  by  inspiration,  that  is,  by  the  inflation  of  the  alveoli.  The 
larger  plates  are  formed  by  the  subsequent  blending  of  several  smaller  ones.  The 
alveoli  of  old  embryos  and  in  stillborn  children  contain  only  cubical  cells. 
The  walls  of  the  alveolar  ducts  and  the  alveoli,  in  addition  to  the  previously 
mentioned  muscle-fibers  in  the  former,  are  composed  of  a  delicate  fibrous 
framework  and  many  elastic  fibers.  The  latter  are  circularly  arranged  in  the 
alveolar  ducts,  and  encircle  the  entrance  to  the  alveolus  (the  mouth  or  base)  ; 
delicate  fibers  spring  from  this  annular  bundle  and  form  a  network  surround- 
ing and  supporting  the  entire  wall  of  the  alveolus.  The  elastic  rings  of  neigh- 
boring alveoli  grow  together  at  the  points  of  contact  and  thus  constitute  the 
alveolar  septa. 

The  areolar  tissue  between  the  lobules  of  the  lung — the  interlobular  con- 
nective tissue — contains  extremely  fine  elastic  fibers  and  a  few  connective-tissue 
cells,  and  in  the  adult  black  pigment-granules  and  inhaled  carbonaceous  parti- 
cles. In  children  the  interlobular  connective  tissue  is  more  richly  developed 
and  the  demarcation  of  the  lobules  more  distinct. 

The  surface  of  the  lung  is  covered  by  the  visceral  pleura  ;  this  is  composed 
of  connective-tissue,  numerous  fine  elastic  fibers,  and  on  its  free  surface  is 
clothed  by  a  simple  stratum  of  flat  polygonal  epithelial  (endothelial)  cells. 
The  parietal  pleura  has  the  same  structure,  but  contains  fewer  elastic  fibers. 

The  blood-vessels  of  the  lungs,  the  branches  of  the  pulmonary  artery,  enter 
at  the  hilus  of  the  lung  and  run  beside  the  bronchi,  bronchioles,  alveolar  ducts, 
and  between  the  infundibula,  where  they  break  up  into  a  very  narrow-meshed 
capillary  network,  placed  immediately  beneath  the  respiratory  epithelium  of 
the  terminal  bronchioles,  the  alveolar  ducts,  and  the  alveoli.  The  veins  arise 
each  at  the  base  of  an  alveolus,  and  unite  into  branches  that  follow  the  bronchi 
and  arteries.  The  walls  of  the  bronchi  are  supplied  by  the  bronchial  arteries, 
which  furnish  a  deep  capillary  plexus  for  the  muscles  and  the  glands,  a  superficial 


THE    RESPIRATORY    ORGANS. 


1S9 


plexus  for  the  tunica  propria.     These  capillaries  are  taken   up  in  part  by  the 
bronchial  veins,  in  part  by  the  pulmonary  veins. 

Of  the  lymphatic  vessels  two  groups  are  recognized,  a  well-developed 
superficial  plexus  beneath  the  pleura  and  a  wide-meshed  deep  plexus  in  the 
interlobular  connective  tissue.  From 
these  networks  small  stems  furnished 
with  valves  proceed,  which  follow 
the  bronchi  and  emerge  at  the 
hilus,  where  they  connect  with  the 
bronchial  lymph-nodules. 

The  numerous  nerves  of  the 
lungs,  derived  from  the  symi)athetic 
and  the  vagus,  contain  meduUated 
and  nonmedullated  nerve-fibers  and 
small  groups  of  ganglion-cells.  The  nerve-endings  stand  in  especial  relation 
to  the  walls  of  the  blood-vessels. 


Capillari 


Fig.  171. — From    a    Section  op  Lung  of  Child, 

InJBCTFD  THKOUr.H    PuLMONARY    ArTBRY.        X    80. 

Of  the  five  alveoli  ilrawn  the  three  upper  ones  are 
fully  injected.    Techn.  No.  126. 


THE  THYROID  GLAND. 
The  thyroid  body  is  a  compound  tubular  gland,  whose  excretory  canal, 
the  thyro-glossal  duct,   opening  at  the  foramen  cecum  of  the  tongue,   with 


Colloid  substa 


Fig.  172.— a  Lob 


Thin  Section 


Thvkoid   Kodv  op 
Icchn.  No.  127. 


Tangential  seciion  of 
lubiile ;  ihc  cpiihc- 
Hum  viewed  from 
the  free  surface. 


the  exception  of  a  few  atrophic  remains  was  obliterated  in  the  embryonic 
stages  of  the  organ.  It  consists,  therefore,  of  completely  closed  tubules ,  which 
are  united  into  lobules  by  loose  connective  tissue.  The  tubirles  differ  greatly 
in  size  (40  to  120 /i  in  diameter)  and  are  lined  by  a  simple  layer  of  cubical 
epithelial  cells.      Their  contents  consists  of  a  characteristic,  homogeneous,  vis- 


19° 


HISTOLOGY. 


cid  mass,  the  colloid  substance,  which  is  found  also  in  the  lymph-vessels  of  the 
organ.  The  blood-vessels  are  exceptionally  numerous,  and  break  up  into  capil- 
laries which  form  a  network  close  beneath  the  epithelium.  The  lymphatics,  like- 
wise profuse,  form  a  network  lying  between  the  tubules.     The  nen-es  follow  the 


Blood-vessels. 
Fig.  173.— Section  of  Sbcondary  Lobiiles  of  Thymus  Body  of 
The  lower  lobules  are  sectioned  tangentially,  so  that  chiefly  only  ( 


Techn.  No.  128. 


ramifications  of  the  blood-vessels  and  form  networks  distributed  especially  to 
the  vascular  walls,  some  of  which  also  surround  the  gland-tubules.  The  pene- 
tration of  the  terminal  twigs  into  the  epithelium  has  not  been  observed. 


THE  THYMUS  BODY. 
The  thymus  body,  in  its  first  anlage  an  epithelial  organ,  consists  in  child- 
hood of  lobes  4  to  1 1  mm.  large,  which  are  enveloped  by  a  fibrous  connective- 
tissue  sheath  containing  fine  elastic  fibers. 
The  capsule  sends  septa  into  the  lobes,  by 
which   a   subdivision   into  smaller    (secon- 
dary)  lobules,    I    mm.    large,    is    effected. 
Each   of   the    lobules    consists  of   adenoid 
tissue,  denser  at  the  periphery  than  in  the 
center,  so  that  a  darker  cortical   zone  and 
a  lighter  medullary  substance  may  be  dis- 
tinguished.   In  the  medullary  substance  con- 
centrically striated   bodies,  varying  greatly 
in    number    and    size    (15    to    180   /i    in 
diameter),   are  found  ;  they  are  masses  of 
altered  epithelial  cells  [the  remains  of  the  epithelial  structures  which  in  the 
embryonic  stages  constituted   the  principal   bulk   of  the  organ].     They  are 
called  Hassair s  corpiisdes. 


THE    URINARY    OROANS.  I9I 

The  blood-vessels  are  richly  developed  and  supply  the  cortex  and  the 
medulla  with  capillary  networks.  The  lymphatics,  likewise,  are  very  numerous  ; 
the  larger  vessels  lie  on  the  surface  of  the  organ,  their  branches  run  in  the  in- 
terlobular septa  and  penetrate  into  the  medullary  substance. 

At  a  later  period  the  tissue  of  the  thymus  undergoes  retrogressive  change ; 
the  greater  jjart  of  the  adenoid  structures  disai)pear  and  are  replaced  by  fat. 


VII.  THE  URINARY  ORGANS. 

THE    KIDNEYS. 

The  kidneys  are  compound  tubular  glands,  which  consist  e.Kclusively  of 
minute  tubes,  the  uriniferous  tubules.  The  niacroscopically  perceptible  dif- 
ferences between  the  peripheral  and  central  portions  of  the  organ,  the  so-called 
cortica/  3ini\  meilulhify  regions,  are  princijially  determined  by  the  course  of  the 
uriniferous  tubules,  the  divisions  within  the  cortex  pursuing  a  tortuous,  those 
within  the  medulla  a  straight  course. 

Each  uriniferous  tubule  begins  in  the  cortex  a.s  a  spherical  dilatation,  the 
Malpighian  corpuscle,  which  is  marked  off  by  a  constriction,  the  neck,  from  the 
greatly  convoluted  succeeding  division,  the  proximal  convoluted  tubule.  This 
passes  into  a  straight  portion,  which  is  at  first  centrally  directed,  but  soon 
turns  back  and  forms  a  loop,  Henle's  loop,  in  which  a  descending  and  an  ascend- 
ing limb  may  be  distinguished.  The  latter  passes  into  a  convoluted  portion, 
the  intercalated  tubule  {irregular  and  distal  convoluted  portions),  that  as  it  pro- 
ceeds assumes  a  straight  course,  and  is  then  called  collecting  tubule  (Fig.  175). 
The  collecting  tubules,  during  their  centrally-directed  course,  take  up  other 
distal  convoluted  tubules,  unite  under  acute  angles  with  neighboring  collect- 
ing tubules,  and  converge  toward  the  apex  of  a  renal  papilla,  where,  diminished 
in  number  but  greatly  increased  in  diameter,  they  terminate  in  the  papillary 
duct  or  duct  of  Bellini,  which  opens  on  the  free  surface  of  the  papilla.  Henle's 
loop-tubules  and  the  collecting  tubules  are  named  straight  tubules  (tubuli 
recti).  Each  uriniferous  tubule  pursues  a  completely  isolated  course  until  it 
is  taken  up  by  a  collecting  tubule.  The  loops  of  Henle  and  the  peripheral 
portions  of  the  collecting  tubules  are  grouped  into  bundles  as  they  ])ass  toward 
the  medulla,  and  form  the  familiar  strife  in  the  cortex  known  as  medullary  rays 
or  pyramids  of  Ferrein. 

The  minute  structure  of  the  uriniferous  tubules  varies  so  greatly  in  the  sev- 
eral divisions  that  a  special  consideration  of  each  is  necessary. 

The  Malf>igliian  corpuscles,  from  0.13  to  0.22  mm.  in  size,  consist  of  a 
spherical  mass  of  convoluted  blood-vessels,  the  glomerulus,  and  the  expanded 
and  invaginated  blind  initial  extremity  of  a  uriniferous  tubule,  the  capsule  of 


192 


HISTOLOGY. 


Boivinaii.  The  glomerulus  lies  within  the  invaginated  portion  of  the  capsule, 
and  is  almost  completely  enveloped  by  it.  Accordingly,  two  layers  are  distin- 
guished in  the  capsule  of  Bowman,  an  inner  (quasi  visceral)  which  lies  close 


Fig.  17s.— Scheme  of  ti 
IFEROUS  Tubules  (Le 
-  (Righ: 

of  kidney  of  an  infant 
Cortex.  M.  Medulla.  7n.s.  Medullary  rays,  /i, 
l^Jz-  Three  renal  lobules,  a  ftlalpighian  corpuscle  ; 
^,  proximal  convoluted  tubule;  c,  descending,  rf,  as- 
cending limb  of  Henle's  loop-tube  ;  e,  distal  convo- 
luted tubule;  /",  collecting  tubule  ;  yi,  portions  of  col- 
lecting tubules;  ^,  excretory  duct.  i.  Branch  of 
renal  artery.  2.  Interlobular  artery.  3.  Afferent 
artery.  4.  Efferent  artery.  5.  Interlobular  vein. 
6.  Branch  of  renal  vein,  x  and  xx.  Branches  sup- 
plying the  medulla. 


Fig.  176.  —  Urin 
Weeks'-Old  F 
pighian  corpuscle, 
f.  Henle's  loop,  de 
f.  Collecting    tubule. 


No. 


g.  Papillary    d 


[29. 


upon  the  glomerulus,  and  an  outer  (quasi  parietal)  layer  ;  the  former,  in  young 
animals,  is  composed  of  cubical  cells,  which  later  become  more  and  more  flat- 
tened, the  latter  of  flat  polygonal  cells  (Fig.  178).  At  the  neck  of  the  capsule 
the  outer  layer  passes  over  into  the   walls  of  the  proximal  convoluted  titlmle, 


THE    URINARY    ORGANS. 


193 


which  is  40  to  60  .a  thick.  The  cells  in  a  condition  of  functional  activity  are 
tall  and  exhibit  a  clear  central  zone  surrounding  the  nucleus,  while  the  outer 
zone  or  ba.se  is  striated,  with  the  strife  placed  radially  to  the  narrow  lumen  ;  in 


i  *^Jti'.—'    '        '^ 


Renal  (Malpighian)  corpuscle 


Medullary  ray. 


Running     at     the 
boundary  be- 


Compare 
Fig.  '75- 


Henle's  loop. 


k  Section  of  Human  Kidney.  Including  a  Portion  op  the  Cortex 
At  X  two  renal  cor|)UScles  iiave  fallen  out.     X  ao.     Techn.  No.  130. 


an  exhausted  condition  the  cells  are  lower,  dim,  their  boundaries  arc  indis- 
tinctly defined,  and  the  free  surface  presents  a  striated  border.  Both  stages  of 
secretion  occur  simultaneously.  The  de- 
sceitdiiii;  limb  of  Henle's  loop  is  9  to  15  /i 
thick,  and  the  lumen  is  very  wide ;  it  is 
lined  by  squamous  epithelial  cells  whose 
nuclei  often  protrude  into  the  lumen.  The 
ascendiiii;  limh  is  23  to  28  11  thick,  and  the 
lumen  relatively  narrower ;  the  epithelial 
cells  resemble  those  of  the  convoluted  divi- 
sions, but  are  somewhat  lower.  The  transi- 
tion of  the  narrow  descending  limb  into  the 
thicker  ascending  portion  does  not  always 
occur  at  the  loop.  The  intercalated  or 
distal  convoluted  portion  is  from  39  to  46  ft. 
thick,  and  the  epithelial  cells  are  cylindrical  or  conical  in  shape  and  have  a 
peculiar  luster.  The  collecting  ttibiiles  increase  in  thickness  as  they  approach 
theajjcx  of  the  pajjilla  ;  the  thinnest  have  a  diameter  of  45  n,  the  thickest  (duct 


Urinlfen 


tubule 


'lo.  178— Scheme.  On  the  left  an  artery 
which  eives  off  an  afferent  vessel  toward 
the  rit;ht ;  this  breaks  up  into  branches, 
which  turn  into  the  radicles  of  the  efferent 
vessel  (directed  toward  the  right).  The 
three  loops  are  intended  to  represent  the 
glomerulus:  this  lies  in  Bowman's  capsule, 
of  which  both  layers  are  visible  :  below,  th<: 
latter  passes  into  the  uriniferous  tubule. 


194 


HISTOLOGY. 


of  Bellini)  of  from  200  to  300  11.  Their  epithelial  cells  are  in  part  clear,  in 
part  granular  columnar  elements,  which  increase  in  height  with  the  increase  of 
the  diameter  of  the  tubule  (Fig.  181,  3). 

The  uriniferous  tubules  are  covered  in  their  entire  length  by  a  structureless 
membrana  propria  situated  outside  of  the  epithelium,  which  is  thickest  in 
the  descending  limb  of  Henle's  loop.     The  tubules  are  enveloped  by  a  small 


V?-^,('A'V!»*/'','«-»  Jjrmri. cowman  s  c 


Bowman's  capsule 


Fig.  179. — Fr 


Mouse.      X  240- 


amount  of  loose  connective  tissue  (interstitial  connective  tissue),  which  at  the 
surface  of  the  kidney  becomes  condensed  and  forms  a  fibrous  investment  con- 
taining plain  muscle-fibers.  The  blood-vessels  run  in  the  interstitial  connective 
tissue. 

The  blood-vessels  of  the  kiJneys.     The  renal  artery  divides  in  the  hilus  of 
the  kidney  into  branches,  which  after  giving  off  small  twigs  to  the  capsule  and 


IG.  180.- 

-A. 

I  so 

LATED  Ch; 

VO LUTED  T 

UBUl 

LE.    Theb; 

into  min 

ute 

rods 

>.     B.  Trai 

mai  convoluted 

tubule :  th 

cate  stri: 

e. 

Both  preparati 

ney.     X 

24( 

rechn.  No. 

;  from  a  cat's  kid- 


''iG.  181. — From  a  Transverse  Section  of  the 
Medulla  of  Human  Kidney,  through  the  Base 
OF  A  Papilla.  X  240.  1.  Descending;  2,  ascend- 
ding  limb  of  Henle's  loop;  3,  collecting  tubule ;  4, 
blood-vessel  filled  with  blood-corpuscles.  Techn. 
No.  130. 


to  the  calices  of  the  kidney,  enter  the  parenchyma  of  the  organ  at  the  circum- 
ference of  the  papillae,  and  without  branching  pass  to  the  boundary  between 
the  cortex  and  the  medulla.  Here  they  bend  at  right  angles  and  form  arches 
with  the  convexity  toward  the  periphery.  From  the  convex  side  of  the  arches,  at 
regular  intervals,  spring  branches  running  toward  the  periphery  ;   these  are  the 


THE    URINARV    ORGANS. 


195 


interlobular  arteries,^-  which  give  off  short  lateral  twigs,  each  one  of  which  sup- 
plies the  afferent  vessel oi  a  glomerulus.  The  glomeruli  ari.se  by  the  rapid  division 
of  the  afferent  artery  into  groups  of  convoluted  capillaries,  which  reunite  into  a 
single  vessel,  the  efferent  artery,  which  is  somewhat  smaller  than  the  entering  ves- 
sel.     The  efferent  artery  breaks  up  into  a  capillary  network  with  round  meshes  in 


Interlobular  vein. 
Interlobular  arterj'. 


Afferent  vessel. 
Efferent  vessel. 


Capillary   network    of  a    n 
ray,  with  elongated  meshe: 


KiG.  182. — From  a  Longitudinal  Suction  op  Injected  Kidnf.y  of  Guinea-Pic.    Techn.  No.  133, 


^•^■^i,. M.ilpighian  corpuscle 


Nervous  network  of  an  interlobular  artery.  ... 


Silvered  uriniferous  tubule. 
Fic.  183.— Section  of  Kidney  <if  Mouse.    X  i8o.    Techn.  No.  134. 

the  region  of  the  convoluted  tubules,  with  elongated  meshes  in  the  region  of  the 
medullary  rays.     From  the  latter  the  veins  arise,  interlobular  veins,  which  lie 

*  Microscopic  regions  of  the  kidney,  with  ill-defined  boundaries,  in  the  axis  of  which  lies 
a  medullary  ray,  and  at  the  periphery  of  which  interlobular  arteries  ascend,  are  designated  lob- 
ules. In  Kig.  175  three  lobules,  /,,  /.„  /,,  are  indicated  by  dotted  lines.  These  lobules  have  no 
relation  whatever  to  the  lobules  of  the  kidney  during  fetal  life. 


196  HISTOLOGY. 

close  beside  the  interlobular  arteries  and  follow  them  throughout  their  course. 
The  vessels  of  the  peripheral  zone  of  the  cortex  converge  to  certain  points, 
where  they  unite  into  radicles  arranged  in  a  stellate  form,  the  veitce  stellatce, 
which  join  the  interlobular  veins  (Fig.  175  and  Fig.  182). 

The  medulla  receives  its  blood  supply  from  the  arterice  recta,  which  arise 
from  the  arterial  arches  at  the  juncture  of  the  medulla  and  the  cortex,  from 
the  efferent  vessels  of  the  most  deeply  situated — and  also  the  largest — glomeruli, 
and  direct  from  centrally-running  branches  of  the  interlobular  arteries.  The 
veins  of  the  medulla  take  their  origin  from  the  wide-meshed  capillary  network 
surrounding  the  large  excretory  ducts  and  join  the  venous  arches  at  the  juncture 
of  the  medulla  and  the  cortex. 

The  lymph-vessels  run  in  part  superficially,  in  the  capsule,  and  in  part 
accompany  the  arteries  in  the   parenchyma  of  the  organ.     The  nerves  form 


Fig.  184.— Transverse  Section  of  the  Lower  Half  of  Human  Ureter.  X  '5-  '■  Epithelium  :  t,  tunica 
propria  ;  s,  submucosa  ;  /,  inner  longitudinal  muscle-bundles  :  r,  circular  layer  of  muscle-bundles  ;  /i,  acces- 
sory outer  longitudinai  muscle-bundles.     Techn.  No.  135. 

plexuses  which  surround  the  arteries  as  far  as  the  Malpighian  corpuscles ;    in 
connection  with  the  uriniferous  tubules  no  nerves  have  as  yet  been  found. 


THE  URETf:RS. 

The  ureters,  the  calices,  and  the  pelvis  of  the  kidney  are  composed  of  three 
coats,  the  mucous  membrane,  which  lies  innermost,  the  muscular  coat,  and  sur- 
rounding this  the  outer  fibrous  coat  (Fig.  184). 

The  tunica  propria  of  the  mucous  membrane  consists  of  delicate  connective- 
tissue  fibers,  which,  richly  interspersed  with  cellular  elements,  passes  without 
sharp  demarcation  into  the  tissue  of  the  submucosa.  The  epithelium  covering 
the  tunica  propria  is  the  so-called  'transitional  epithelium  ;  "  that  is,  a  stratified 
scaly  epithelium  composed  of  but  few  layers,  of  which  the  uppermost  layer  con- 
sists of  cylindrical  or  cubical,  only  slightly  flattened  elements.      Occasionally, 


THE    URINARY    ORGANS.  197 

instead  of  the  latter,  large  plate-like  cells  are  present,  which  contain  several 
nuclei  that  have  arisen  by  amitotic  division. 

The  muscular  coat  consists  of  an  inner  longitudinal  and  an  outer  circular 
layer  of  smooth  muscle-fibers,  which  in  the  lower  half  of  the  ureter  possesses  an 
additional  discontinuous  outer  layer  of  longitudinally-arranged  muscle-bundles. 

'Y\\Q  fibrous  (-(w/ consists  of  loosely-united  connective- tissue  bundles. 

The  mucous  membrane  of  the  calices  is  continued  over  the  surface  of  the 
renal  papilife,  the  circular  muscle-fibers  form  a  sphincter  muscle  around  the 
papilla;. 

Both  the  blood-  and  the  lymph-vessels  are  especially  numerous  in  the 
mucous  coat.  The  nerves  are  distributed  principally  to  the  muscular  coat ; 
single  fibers  extend  into  the  tunica  propria  as  far  as  the  epithelium. 


Fig.  185. — Portion  of  a  Vkktical  Section  op   Human  Vesical  Mucous  I^Iemdrane.    X  560.     Techn 

No.  136. 


THE  URINARY  BL.\DDER. 

The  urinary  bladder  likewise  consists  of  a  mucous,  a  muscular,  and  a 
fibrous  coat.  The  epithelium  resembles  that  of  the  ureter  and  the  pelvis  of  the 
kidney  in  every  particular;  a  distinction  from  these  is  impossible.  The  tunica 
l)ropria  occasionally  contains  solitary  lymph-nodules.  The  muscular  coat  con- 
sists of  strata  of  smooth  muscle-fibers,  an  inner  and  an  outer  longitudinal 
layer,  which  enclose  between  them  a  circular  layer.  The  layers  interlace  in 
such  a  manner  that  it  is  not  possible  to  define  their  exact  limits.  At  the  base 
of  the  bladder  the  inner  longitudinal  layer  is  augmented,  the  circular  layer 
forms  the  not  always  distinct  internal  vesical  sphincter.  Blood-  and  lymph- 
vessels  have  the  same  distribution  as  in  the  ureter;  microscopic  groups  of  gang- 
lion-cells are  situated  along  the  course  of  the  nerves. 

In  the  tunica  propria  of  the  lower  division  of  the  pelvis  of  the  kidney, 
the  upper  jwrtion  of  the  ureter  and  the  bladder  round  or  oval  bodies  occur, 
which  have  been  erroneously  regarded  as  glands.  They  are  sprouts  of  the  surface 
epithelium,  possess  the  same  structure,  are  without  a  lumen,  and  occasionally 
have  even  severed  their  connection  with  the  superficial  epithelium. 


I  go  HISTOLOGY. 

THE    URETHRA. 

'Y\\t  female  urethra  is  composed  of  a  mucous  coat  and  a  robust  muscular 
coat.  The  tunica  propria  consists  of  delicate  fibrous  connective  tissue  contain- 
ing numerous  connective-tissue  cells,  and  is  beset  \yith  papillee,  that  are  especially 
well  developed  near  the  meatus.  The  epithelium  varies,  in  some  individuals  it  is  a 
stratified  scaly,  in  others  a  simple  columnar  epithelium.  A  few  branched  simple 
tubular  glands  are  present ;  they  occur  in  small  groups  at  the  meatus,  and  are 
called  "  periurethral  "  glands.  The  muscular  coat  consists  of  an  inner  longi- 
tudinal and  an  outer  circular  layer  of  nonstriped  muscle-fibers,  between  which 
extends  a  compact  fibrous  connective  tissue  containing  many  elastic  fibers.  The 
mucous  coat  is  richly  supplied  with  veins. 

The  male  urethra  (better,  male  urogenital  sinus)  is  likewise  composed  of  a 
mucous  coat  and  a  muscular  coat,  but  they  vary  in  structure  in  the  different 
parts  of  the  canal.  In  the  prostatic  portion  the  epithelium  resembles  that  of 
the  bladder;  in  the  membranous  division  it  gradually  passes  into  the  stratified 
columnar  variety,  which  in  the  spongy  part  is  transformed  to  a  simple  columnar 
epithelium.  From  the  fossa  navicularis  on,  the  epithelium  is  of  the  stratified 
squamous  type.  The  tunica  propria  is  rich  in  elastic  fibers  and  is  beset  with 
papillae,  that  are  especially  well  developed  in  the  fossa  navicularis.  Isolated 
branched  simple  tubular  glands  (Littre's  glands)  occur  throughout  the  entire 
urethra.  The  muscular  coat,  in  the  prostatic  division,  consists  of  an  inner 
longitudinal  and  an  outer  circular  layer  of  smpoth  muscle-fibers  ;  both  layers 
are  still  well  defined  in  the  membranous  portion,  but  gradually  cease  in  the 
spongy  portion,  where  the  circular  layer,  still  conspicuous  in  the  bulbous  ure- 
thrte,  is  the  first  to  disappear  ;  in  the  anterior  part  of  the  spongy  division  a  few 
oblique  and  longitudinal  bundles  occur  (Fig.  193).  The  mucous  membrane 
has  a  rich  vascular  supply.      The  lymph-vessels  lie  beneath  the  blood-vessels. 


VIII.  THE  REPRODUCTIVE  ORGANS. 

THE  MALE  REPRODUCTIVE  ORGANS. 

THE  TESTICLE. 
The  testicles  are  compound  tubular  glands,  which  are  enveloped  in  a 
connective-tissue  capsule.  This  capsule,  the  tunica  albuginea,  is  a  tough 
membrane  which  encloses  the  parenchyma  and  on  the  posterior  upper  aspect 
is  greatly  thickened,  forming  a  mass,  the  corpus  Highmori  or  mediastinum, 
which  juts  into  the  interior  of  the  organ.  From  this  a  number  of  septa 
arise,  which  pass  along  divergent  paths  to  the  tunica  albuginea  and  so 
divide  the  parenchyma  of  the  testicle  into  pyramidal  lobules,  with  their  base 
directed  toward  the  capsule,  tlieir  apex  toward  the  corpus   Highmori.     The 


THE  MALE  REPRODUCTIVE  ORGANS. 


199 


tunica  albuginea  consists  of  dense  fibrous  connective  tissue,  which  on  its  free 
surface  (the  visceral  layer  of  the  tunica  vaginalis)  is  covered  by  a  simple  layer 
of  flat  epithelial  cells,  on  its  inner  surface  is  in  contact  with  a  layer  of  loose 
connective  tissue,  which  supports  numerous  blood-vessels  and  is  called  hinica 
vasculosa ;  the  latter  is  connected  with  the  interlobular  septa.  The  corpus 
Highmori  is  a  dense  connective-tissue  structure  and  encloses  a  network  of 
freely-anastomosing  tubules,  the  rete  testis.  The  septa  consist  of  bundles  of 
connective  tissue  which  are  continuous  with  the  connective  tissue  surrounding 
the  individual  .seminiferous  tubules.  This  "interstitial"  connective  tissue  is 
rich  in  cellular  elements,  the  so-called  interstitial  cells,  which  are  in  part  flat 


taining  the 


Fig.  186.— Cross-Section  of  Testicle 


Tcchn.  No.  140. 


connective-tissue   cells,    in   part  spherical   cells   containing   pigment   or   fatty 
granules. 

The  seminiferous  tubules  may  be  divided  into  three  portions  :  they  begin  as 
(i)  the  convoluted  tubules,  which  pass  into  (2)  the  straight  tubules,  which  con- 
tinue as  (3)  the  rete  testis.  The  convoluted  tubules  are  round,  winding  canals, 
about  140  II  in  diameter.  Their  initial  extremity  has  not  yet  been  definitely 
located  ;  probably  they  are  united  with  one  another  at  the  periphery, 
beneath  the  tunica  vasculosa,  and  form  a  network  from  which  numerous  tubules 
turn  a.side  and  with  many  windings  pa.ss  toward  the  corpus  Highmori.  Tubules 
with  blind  ends  have  been  observed.      During  their  course  the  tubules  unite 


200  HISTOLOGY. 

with  one  another  and  diminish  in  number.  Not  far  from  the  corpus  Highmori 
the  convohited  tubules  pass  into  the  straight  tubules,  which,  considerably  re- 
duced in  size  (20  to  25  /j  thick),  after  a  short  course  penetrate  into  the 
mediastinum  and  form  the  rete  testis,  the  tubules  of  which  measure  from  24 
to  180  //. 

The  walls  of  the  convohifed tiilniles  from  without  inward  consist  of  (i) 
several  layers  of  flattened  endothelioid  connective-tissue  cells;  (2)  a  thin 
membrana  propria;  and  (3)  of  a  stratified  epithelium  the  character  of  which 
varies  greatly  in  the  several  divisions  of  the  tubules.  When  the  gland  is  in  a 
condition  of  rest  several  strata  of  spherical  cells,  whose  nuclei  stain  more  or 
less  intensely,  may  be  seen  lining  the  tubules  (Fig.  187).  In  a  condition  of 
activity  the  epithelium  exhibits  a  cycle  of  phenomena  relating  to  spermatogenesis. 
The  cells  lying  next  to  the  basement  membrane — -parietal  stratum — are  of  two 
kinds  :  the  sustentaailar  cells  or  Sertoli's  columns,  which  take  no  direct  part  in 
the  production  of  the  seminal  filaments,  and  the  spcrmatogcnic  cells,  the  real 


.-.'■."'-■.■■:5,    .■'..'s'^.f  r '^'--A  \  '-^ 


:,      ■;        Epithelium    in 


G.  1S7. — From  a  Cross-Sbction 
epithelium  has  become  sol 
tissue.     Techn.  No.  141. 


"M 


F  Ox.     X  50.     In  the  processes  of  fixitig  and  hardening  the 
that  spaces  occur  between  it  and  the  interstitial  r — — *••— 


producers  of  the  semen.  They  multiply  by  indirect  division,  and  grow  to  be 
large  cells,  that  occupy  the  next  layer  within.  These  are  the  mother-cells, 
which  divide  twice,  each  giving  rise  to  four  daughter-cells  lying  in  a  zone  still 
nearer  to  the  center  of  the  tubule.  The  latter  are  the  spermatids  and  from 
them  the  spermatozoa  are  directly  derived.  The  nucleus  of  each  spermatid 
develops  into  the  head  of  a  spermatozoon,  a  small  portion  of  the  protoplasm 
forming  the  caudal  filament.  The  middle-piece  reacts  like  paranuclein  and 
probably  is  derived  from  the  centrosome.  While  these  changes  are  in  progress 
the  columns  of  Sertoli  grow  in  length  centrad  and  a  large  number  of  spermatids 
form  a  connection  with  each  one  of  them  ;  it  is  highly  probable  that  by  means 
of  this  connection  the  spermatids  receive  their  nutritive  material. 

The  walls  of  the  tulntli  recti  consist  of  a  membrana  propria  and  within  this 
of  a  simple  layer  of  low  columnar  cells. 

The  canals  of  the  rctc  testis  are  lined  l)y  a  simple  stratum  of  cubical  or  flat 
epithelial  cells. 


THE    MALE    REPRODUCTIVE    ORCiANS.  20I 

The  arteries  of  the  testicles  are  branches  of  the  spermatic  artery,  which 
proceed  in  part  from  the  mediastinum  and  in  part  from  the  tunica  vasculosa  to 
the  intertubular  septa,  and  then  break  up  into  capillary  networks  which  sur- 
round the  seminiferous  tubules.  The  veins  follow  the  course  of  the  arteries. 
The  lytnph-vessels  form  a  plexus  beneath  the  tunica  albuginea,  which  is  in  con- 
nection with  a  network  of  lymph-capillaries  enveloping  the  seminiferous  tubules. 
The  nerves  form  networks  about  the  blood-vessels,  from  which  single  fibers  are 
said  to  branch  off,  pierce  the  membrana  propria,  and  terminate  in  club-shaped 
endings  between  the  e])ithelial  cells. 


Fig.  i88. — Cross-Section  oi 
M  6rst  round  nuclei  of  th' 
into  the  heads  of  the  sem 


A  Seminiferous  Ti'bule  of  Mouse.  X  360.  Below  on  the  lefi  ; 
spermatids,  which  become  oval  (above),  and  are  transformed  (below  c 
lal  filaments.    Techn.  No.  143. 


TH1-:  SEMEN. 
The  secretion  of  the  testicles,  the  semen,  consists  almost  exclusively  of 
spermatozoa,  structures  in  which  a  head  and  a  tail  are  distinguished.  In  man 
the  head  is  3  to  5  /i  long  and  2  to  3  /j  broad,  flattened,  seen  from  the  side 
pyriform  in  shape,  with  the  narrow  end  directed  forward,  seen  on  its  broadest 
surface  oval,  with  the  anterior  end  rounded.  The  /(///when  very  highly  magni- 
fied exhibits  a  delicate  filament  extending  from  end  to  end,  the  axial  fiber, 
which  is  composed  of  delicate  fibrils.      Three  divisions  are  recognized  in  the 


20  2  HISTOLOGY. 

tail :  the  middle-piece,  lying  next  to  the  head,  6  tx  long  and  scarce  i  ij.  broad  ; 
following  this  the  main-piece,  40  to  60  ji  long  and  gradually  diminishing  in 
thickness  ;  the  tip  of  the  tail,  the  end-piece,  is  about  10  /i  long  and  consists 
of  the  projecting  axial  fiber. 

The  different  forms  of  spermatozoa  in  animals  cannot  be  described  here. 
In  birds  and  tailed  amphibians  a  spiral  fiber,  united  to  the  axial  fiber  by  a 
hyaline  membrane,  has  been  discovered ;  it  has  also  been  found  in  the  rat 
and  other  mammals,  but  has  not  been  demonstrated  with  certainty  in  man. 

The  spermatozoa  are  distinguished  by  their  extraordinary  vitality  (probably 
due  to  the  calcareous  matters  which  they  contain). 

The  vibratile  movements  of  the  spermatozoa  are  executed  by  the  cilium 
alone,  which  propels  the  head  before  it ;  they  seldom  occur  in  the  con- 
centrated secretion  of  the  testicle,  and  first  begin  only  after  dilution  normally 
effected  by  admixture  of  the  fluids  of  the 
ampullae,  of  the  seminal  vesicles,  of  the 
prostate  gland,  and  of  Cowper's  glands.  In 
this  mixture  of  fluids  the  motions  may  con- 
tinue 24  to  48  hours  after  death,  and  for  a 
still  longer  period  in  the  secretions  of  the 
female  generative  tract.  Water  paralyzes  the 
movement,  which,  however,  may  be  stimu- 
lated to  renewed  activity  by  the  addition 
of  normal  animal  fluids  of  alkaline  reaction 
and  moderate  concentration  ;  normal  fluids  in 
general,  also  a  one  per  cent,  salt  solution  exert 
a  favorable  influence  on  the  vibrations  of  the 
spermatozoa,  while  acids  and  metallic  salts 
suspend  them.  In  motionless  spermatozoa  the 
caudal  filament  is  frequently  looped  (Fig.  189,  3). 


THE  EXCRETORY  DUCTS  OF  THE  TESTICLE. 

The  excretory  ducts  of  the  testicle  include  the  epididymis,  vas  deferens, 
the  seminal  vesicles,  and  the  ejaculatory  duct.  (The  tubuli  recti  and  rete 
testis  belong  to  the  excretory  ducts,  but  were  described  with  the  gland  because 
they  are  enclosed  within  it. )  From  the  upper  end  of  the  rete  testis  about  fifteen 
vasa  efferentia  emerge,  which  by  their  progressively-increasing  convolutions 
form  as  many  conical  lobules,  the  coni  vasculosi.  The  aggregate  of  the  coni 
constitute  the  globus  major  of  the  epididymis.  By  the  union  of  the  vasa 
efferentia  the  vas  epididymis  zrises,  which  by  its  complex  convolutions  forms  the 
body  and  globus  minor  of  the  epididymis,  and  then  continues  as  the  ras 
deferens. 

The  vasa  efferentia  are  lined  by  an  epithelium  consisting  of  totally  dis- 
similar varieties ;  groups  of  simple  ciliated  cylindrical  elements  alternate 
with  clusters  of  cubical  cells  without  cilia  ;   the   latter  consequently  have  the 


Fig.  189.— 1 

^ilw^ed' 
filament, 
head:    b. 
The  end- 

,2.3.  Human  Spermatozoa. 

.  Viewed  from  the  surface.    2, 

n  profile.     3.  Looped  seminal 

4.  Spermatozoon  of  ox  ;    a, 

middle-piece  ;  c,  main-piece, 
piece  and  the  demarcation  of 

these  parts  cannot 
this  magnification. 

be   perc 
Techn. 

eived    w 
No.  144. 

ith 

THE    MALE    REPRODUCTIVE    ORGANS. 


203 


appearance  of  simple  saccular  glands,  which,  however,  do  not  produce  evagina- 
tions  of  the  membrana  propria  (Fig.  190).  A  fibrous  membrana  propria  and 
a  tunic  of  nonstriped  muscle  consisting  of  several  circular  strata  complete  the 
walls  of  the  vasa  efferentia. 

The  vas  epididymis  possesses  a  stratified  ciliated  epithelium  ;  its  convolu- 
tions are  supported  and  held  together  by  a  loose,  vascular  connective  tissue ; 
toward  the  vas  deferens  the  circular  strata  of  muscle-fibers  increase  in  thickness 
(Fig.  191). 


Fig.  190  — Transvhrsb  Sb 

the  right  is  schematic,     wo  ciiia 
well  preserved.     Techtj.  No.  147. 


t  Adult  Human  Vas  Effekens  Testis.    The  end  of  the  illustration  c 
could  be  seen,  although  those  of  the  epithelium  ol  the  epididymis  we 


The  vas  deferens  consists  either  of  a  two-layered  columnar  epithelium  or 
of  a  transitional  epithelium,  of  a  layer  of  connective  tissue  divided  into  a  tunica 
propria  and  a  submucosa,  and  of  an  inner  circular  and  outer  longitudinal 
stratum  of  smooth  muscle-fibers  (Fig.  192).  In  the  initial  portion  of  the 
vas  deferens  there  is  also  a  thin  layer  of  longitudinal  nonstriped  muscle-fibers 
in   the  submucosa.     The  terminal  portion  expands  forming  the  ampulla,  the 


Stratified  ciliated  epithelium. 


Fig.  191 


VBRSR  Section  of  Human  Epididymis.     X  So.    Techn.  No.  147. 


walls  of  which  are  thinner,  but  exhibit  a  similar  structure.  In  the  mucous 
membrane  of  the  ampulla  are  branched  tubular  glands ;  the  columnar  cells  of 
the  epithelium  contain  numerous  pigment-granules.  The  semitial  vesicles  have 
the  same  structure.  The  ejactilatory  duct  consists  of  a  simple  columnar  epithe- 
lium and  thin  inner  circular  and  outer  longitudinal  strata  of  smooth  muscle- 
fibers. 

The  nerves  form  a  plexus  in  the  niuscularis  of  the  epididymis  and  of  the 
vas  deferens,  denser  in  the  latter,  from  which  delicate  fibers  continue  into  the 
mucous  membrane. 


204  HISTOLOGY. 

T\\t  pamiiiJyiiiis  or  the  oi-gaii  of  Giraldes,  lying  between  the  convoUitions 
of  the  epididymis,  and  likewise  the  vas  aberrans  Hallcri  are  atrophic  remains 
of  the  Wolffian  body.  Both  consist  of  tubules  lined  by  ciliated  cubical  epi- 
thelium and  enveloped  by  a  vascular  connective  tissue.  The  sessile  hydatid  ox 
hydatid  of  Morgagni  is  a  solid  lobule  composed  of  a  highly-vascular  connective 
tissue  and  covered  by  a  ciliated  columnar  epithelium  ;  it  possesses  a  short 
pedicle,  which  contains  a  duct  lined  by  ciliated  columnar  epithelium.  The 
inconstant  stalked  hydatid  is  a  vesicle  lined  by  cubical  epithelial  cells  and  con- 
tains a  clear  fluid.  The  signification  of  the  hydatids  has  not  yet  been  fully 
explained  ;  they  are  by  many  regarded  as  the  remains  of  fetal  organs, — of  the 
pro.ximal  end  of  the  rudimentary  Miillerian  duct. 


t\  \  1 ,  );-^ 


—  Columnar  epithelii 
-  "ir^  Tunica  propria. 
Submucosa. 

Circular  muscle. 


J 
I Longitudinal  muscle 


Fig.  192. — Tkansvbrsh  Section  of  the  Initial  Portion  of  Human  Vas  Dbpbrens.  X  240  The  trans- 
versely-cut longitudinal  muscle-fibers  of  the  submucosa  are  to  be  seen  as  minute  circles  and  dots.  Techn. 
No.  147. 

THE  PROSTATE  BODY. 
The  jjrostate  body  consists  for  the  lesser  part  of  glandular  tissue,  for  the 
greater  part  of  non-striped  muscle- fibers.  The  glandular  portion  is  composed 
of  thirty  to  fifty  simple  branched  tubular  serous  glands,  and  is  characterized  by 
its  loose  structure,  that  is,  the  wide  intervals  between  the  tubules.  The  tubules 
open  by  tw^o  large  and  a  number  of  smaller  ducts  into  the  urethra.  The  gland- 
ular cells  are  low  columnar  elements,  which  in  a  simple  layer  line  the  tubules. 
In  the  larger  ducts  the  epithelium  is  of  the  transitional  variety,  like  that  in  the 
prostatic  portion  of  the  urethra.  In  elderly  persons  the  so-called  prostatic 
crystals — round  stratified  masses  of  secretion  up  to  o.  7  mm.  in  size — occur  in 
the  gland-tubules.  The  involuntary  muscle-fibers,  found  everywhere  in  large 
quantities  between  the  gland-lobules,  are  augmented  toward  the  urethra  and 
form  a  robust  circular  layer  (the  internal  vesical  sphincter)  ;  numerous  invol- 
untary muscle-fibers  are  found  also  on  the  external  surface  of  the  prostate  body, 
where  they  extend  to  the  bundles  of  striated  muscle-fibers  of  the  external 
vesical  sphincter.  The  prostate  gland  and  the  colliculus  seminalis  are  provided 
with  many  blood-vessels.  Regarding  the  terminations  of  the  nerves  nothing 
is  definitelv  known. 


THE    MALE    REPRODUCTIVE    ORGANS. 


205 


The  g/(}>ti/s  of  C(m>/>er  are  compound  tubular  glands,  whose  wide  tubules 
are  clothed  with  a  simple  layer  of  clear  columnar  cells,  and  whose  excretory 
duct  is  lined  with  two  to  three  strata  of  cubical  cells. 


THE  PENIS. 

The  penis  consists  of  three  cylindrical  bodies  :  the  two  corpora  cavernosa 
and  the  corpus  spongiosum,  which  are  enveloped  by  fascia  and  skin. 

Each  corpus  cavernosum  is  composed  of  a  fibrous  sheath,  the  tunica 
albuginea,  and  of  erectile  tissue.  The  tunica  alhuginea  is  a  stout  connective- 
tissue  membrane,  i  mm.  thick,  in  which  an  outer  longitudinal  and  an  inner 
circular  layer  may  be  distinguished  ;  the  bundles  are  intermingled  with  many 


Epilhelil 


Fig.  103. — From  a  Transverse  Section  of  the  Cavernous  Portion  op  the  Human  Urethra.  X  20. 
/.  Littrc's  glands;  the  lowermost  line  indicates  the  body  of  the  gland,  the  upper  lines,  portions  of  the  excre- 
tory duct:  ^.blood-vessels:  wi.  transverse  section  of  longitudinally-disposed  muscle-fibers;  r,  superficial 
cortical  capillary  network.     Tcchn.  No.  148. 


elastic  fibers.  The  erectile  tissue  consists  of  connective-tissue  trabeculoe  con- 
taining bundles  of  smooth  muscle-fibers,  which  by  means  of  numerous  anasto- 
nio.ses  form  a  network  the  spaces  of  which  are  lined  by  a  single  stratum  of 
flat  epithelial  cells.  The  spaces  are  filled  with  venous  blood.  The  thick- 
walled  arteries  pass  in  part  into  capillaries,  in  part  open  directly  into  the  deep 
cortical  plexus.  The  capillaries  form  a  network  beneath  the  tunica  albuginea, 
iht  su/>erjicia/  {fine)  cortical  plexus,  which  is  connected  with  a  many-layered 
net  of  wide  venous  channels,  the  Jeep  {coarse)  cortical  plexus.  This  lies  in 
the  superficial  strata  of  the  erectile  tissue  and  passes  gradually  into  the  venous 
spaces  of  the  latter.  The  so-called  lielicine  arteries  are  small  branches  within 
slender  trabecule;,  which  protrude  as  loops  in  the  cavernous  spaces,  and  in 
an  imperfect  injection  a|)pear  to  terminate  in  blind  ends.  The  veins  which 
return    the    blood    from    the   corpora    cavernosa  arise   mostly   from  the  deep 


2o6  HISTOLOGY. 

cortical  plexus,  in  part  out  of  the  deeper  portions  of  the  erectile  tissue.     They 
penetrate  the  tunica  albuginea  and  empty  into  the  dorsal  vein  of  the  penis. 

The  corpus  spongiosum  consists  of  two  different  divisions ;  the  central  por- 
tion is  a  venous  network  formed  by  the  conspicuously-developed  veins  of  the 
submucosa  of  the  urethra  ;  the  peripheral  portion  resembles  in  structure  the 
corpora  cavernosa,  excepting  that  there  is  no  direct  communication  of  the 
arteries  with  the  venous  spaces.  The  tunica  albuginea  is  composed  of  a  layer 
of  circularly-arranged  bundles  of  fibrous  tissue.  The  glans  consists  of  greatly- 
convoluted  veins,  held  together  by  a  well-developed  connective  tissue  which 
supports  the  arterioles  and  capillaries. 


THE  FEMALE  REPRODUCTIVE  ORGANS. 

THE  OVARIES. 
The  ovaries  consist   of  connective  tissue  and  glandular  substance.     The 
compact  connective  tissue,  the  ovarian  stroma,  is  arranged  in  several  strata ; 


:   Year: 

s  0: 

LD 

X 

lO. 

..  Germi 

inal 

epi 

imost  z 

one 

of'th 

artex 

containi 

ngn 

6,  medulla 

with 

nui 

Tieroi 

js  tortuo 

igerus  n 

ot  w 

ithin 

th< 

:plar 

leofthe 

sect 

ion 

._E  Section  of  the  Ovary  of  a  Child  E 

,  _, a  albuginea,  as  yet  but  slightly  developed  ;  3, 

erous  minute  follicles  :  4,  larger  follicle;  5,  inner  division  of  cor 
ies  :  7,  follicle  cut  at  the  periphery  :  8,  large  follicle,  the  cumulu 
9,  hilus,  containing  wide  veins.     Techn.  No.  149. 

the  outermost,  the  tunica  albuginea,  is  composed  of  two  or  more  lamella;  of 
variously-disposed  bundles,  which  pass  by  imperceptible  gradations  into  the 
stroma  of  the  cortex  ;  the  latter  encloses  the  glandular  substance  and  is  contin- 
uous with  the  medulla,  which  contains  numerous  convoluted  blood-vessels  and 
strands  of  smooth  muscle-fibers  accompanying  them.  'l\\e:  glandular  substance 
is  formed  by  a  profusion  of  spherical  epithelial  sacs,  the  Graafian  follicles,  each  of 
which  contains  an  ovum.  In  the  human  ovary  there  are  about  36,000  follicles. 
The  majority  of  the  follicles  are  microscopic  in  size  (4  ti)  and  in  the  outermost 
stratum  of  the  cortex  form  an  arched  zone  embracing  the  entire  organ  except 
at  the  hilus,  where  the  vessels  and  nerves  enter.     The   larger  follicles  occupy 


THE  FEMALE  REPRODUCTIVE  ORGANS. 


207 


the  deeper  portions  of  the  cortex.  The  largest,  those  readily  perceptible  by 
the  unaided  eye,  when  fully  matured  extend  from  the  medulla  to  the  tunica 
albuginea.  The  surface  of  the  ovary  is  covered  by  a  simple  layer  of  very  small, 
short  cylindrical  cells,  X}cit  germinal  epithelium. 

Only  tlie  initial  stage  in  the  development  of  the  ova  takes  place  during 
the  embryonal  period  ;  their  subsequent  development,  from  the  primordial 
to    the   fully-ripened   follicle,  may  be  observed    in    every  functionally  active 


Gerinin.1l  cpiihcl 
Egg-tubes 


Germinal  spot 
Germinal  vesicle 


Follicular  epithelium 


r  A  Vertical  Section 
has  a  large  nucleus  wi 
Techn.  No.  14Q. 


>F  AH  Ovary  OF  AN  Infant  Four  Weeks  Old.    X  240.    The  prim- 
li  a  nucleolus.    The  egg-tube  contains  three  ova,  surrounded  by  cylin- 


ovary.  In  the  fetal  i)eriod,  and  also  after  birth,  there  may  be  seen  be- 
tween the  columnar  elements  of  the  germinal  epithelium  larger  spherical  cells 
with  nucleolated  nuclei,  the  sexual  cells,  specially  differentiated  elements  of  the 
germinal  ei)ithelium.  In  the  course  of  development  groups  of  cylindrical  epi- 
thelial cells  enclosing  several  sexual  cells  grow  into  the  ovarian  stroma.  These 
groups  are  the  primary  egg-tubes.  Each  ovum  becomes  enveloped  by  a  single 
layer  of  the  small   columnar  cells   and   separated   by  constriction   from  the 


Germinal  epithcliuni 


Fig.  196 


Rabbit.     X  90.    Techn.  No.  149. 


remaining  ova.  It  is  now  a  spherical  body,  the  pi imary  follicle,  which  thus_^ 
consists  of  the  ovum  and  the  epithelial  cells — the  so-called  follicular  epithelium 
— enclosing  it.  So  far  the  developmental  processes  are  chiefly  fetal. .  The 
cells  of  the  follicular  epithelium  now  grow  taller,  multiply,  and  become  strati- 
fied ;  the  ovum  increases  in  size,  takes  up  an  eccentric  position  within  the 
follicle,  and  acquires  a  ])rotecting  membrane,  the  zona  pellucida,  which  exhibits 
delicate  radial  striatioii  and  gradually  augments  in  thickness.      .\s  the  ovum 


HISTOLOGY. 


develops  in  size  a  modification  of  the  protoplasm  occurs  ;  the  greater  part  of 
it  is  transformed  into  a  granular  mass,  the   deiitoplasm  ;   of  the  original  egg- 


Theca  foiliculi 


Ovum  with  zona  pellucida..  germ- 
inal vesicle,  and  germinal  spot. 


Fig.  197.— Section  of  a  Large  Graafian  Follicle  of  a  Child  Eight  Years  Old.      X  9°.      Th'  <:'=; 
space  wilhin  ihe  follicle  contains  the  liquor  foiliculi.     Techn.  No.  149. 


Zona  pellucida 
Vitellus. 


Zona  pellucid.i. 
Vitellu..  • 


^^^^ 


0 


Germinal 
vesicle. 

Germinal  spot. 


(cells  of  the 
mulus). 


Fig.  198.— An  Ovl 


Graafian  Follicl 


of  the  zona  and  the  perivitelline  space  c 


Cow.     A  magnified  50,  B  magnified  240  tii 


protoplasm  there  remains  only  a  small  zone  surrounding  the  eccentrically-situ- 
ated nucleus  and  a  thin  stratum  on  the  surface  of  the  ovum.  The  deutoplasm 
and  egg-protoplasm  are  together   named  viUllus.     The  nucleus   is  called  the 


I'HE    FEMALE    REPRODUCTIVE    ORlJANS.  209 

germinal  vesicle :  it  contains  the  germinal  spot.*  Amceboid  movements  have 
been  observed  in  the  latter.  Between  the  vitelhis  and  zona  pelhicida  a  narrow 
fissure,  1.3  /i  wide,  the  pcrivitelline  space,  has  been  described. 

The  follicle  develops  further  by  continual  multiplication  of  the  cells  of  the 
follicular  epithelium  and  a  cleft  appears  in  their  midst  that  becomes  filled 
with  a  fluid  substance,  the  liquor folliculi.  This  liquid  is  in  part  a  transudate 
from  the  blood-vessels  surrounding  the  follicle,  and  is  in  part  derived  from  the 
liquefaction  of  some  of  the  cells  of  the  follicular  epithelium;  it  increases  pro- 
gressively in  quantity  and  the  follicle  expands  to  a  vesicle — the  Graafian  fol- 
licle— having  a  diameter  of  from  0.5  to  12  mm.  Around  the  larger  follicles 
the  connective  tissue  of  the  stroma  is  arranged  in  circular  lamellae  forming  a 
sheath  called  the  theca  folliculi,  in  which  an  outer  fibrous  layer — tunica  fibrosa — 
and  an  inner  va.scular  layer  rich  in  cells — tunica  propria — may  be  distinguished. 
'I'he  stratified  follicular  epithelium  has  long  been  known  as  the  membrana 
granulosa  ;  at  one  point  it  presents  a  thickening,  the  discus  proligerus  or  cumulus 
oi'igerus,  which  encloses  the  ovum.  The  cells  of  the  cumulus  which  lie  next 
to  the  zona  pellucida  are  radially  placed  to  the  ovum  and  form  the  corona 
radiala  (Fig.  198).  The  greater  part  of  the  interior  space  of  the  follicle  is 
occupied  by  the  liquor  folliculi. 

When  the  Graafian  follicle  has  attained  its  fiill  development,  it  bursts  at 
the  pole  directed  toward  the  surface  of  the  ovary,  where  its  site  is  indicated  by 
the  attenuated  and  arched  overlying  tissue,  and  the  ovum  surrounded  by  the 
discus  escapes  into  the  pelvic  cavity  ;  the  empty  follicle  becomes  converted  into 
the  yellow  body — corpus  luteuni.  When  fertilization  does  not  follow  the  dis- 
charge of  the  ovum  the  yellow  body  disappears  after  a  few  weeks  ;  it  is  called  the 
false  corpus  luteum.  When  the  escape  of  the  ovum  is  followed  by  pregnancy,  the 
ruptured  follicle  develops  into  \.\\t  true  yellon.' body,  which  possesses  a  diameter  of 
about  one  centimeter  and  endures  for  years.  It  consists  of  a  fibrous  membrane 
( the  former  tunica  fibrosa)  enclosing  a  yellow  mass  formed  principally  by  pro- 
liferation of  the  cells  of  the  tunica  propria,  and  of  the  metamorphosed  remains 
of  the  follicular  e])ithelium,  in  the  center  of  which  is  a  cavity  filled  with  blood. 
The  blood  is  derived  from  the  torn  vessels  of  the  tunica  propria.  Later  the 
cells  become  in  part  converted  into  new  connective  tissue,  the  center  becomes 
decolored,  and  in  place  of  the  blood-clot  a  granular  ma.ss  occasionally  con- 
taining hematoidin  crystals  appears. 

Not  all  the  primitive  follicles  attain  complete  development.  Many  undergo 
retrogressive  change.  Retrograde  metamorphosis  of  mature  follicles  also  occurs. 
This  process  is  effected  as  follows  :  first  the  ovum  dies  and  then  cells — in 
l)art  elements  of  the  membrana  granulosa,  in  part  leucocytes — wander  Into  the 
ovum  and  li(iuefy  and  absorb  its  substance.  Having  completed  the  disinte- 
gration and  resorption  of  the  vitelhis,  the  migrated  cells  perish. 

The  arteries  of  the  ovary,  branches  of  the  ovarian  and  uterine  arteries, 


*  Tlie  germinal  spot  cannot  be  regarded  as  a  nucleolus,  since  itdiflers  from  this  in  its  chem- 
al  relations.     It  is  not  composed  of  paranuclein,  but  of  a  substance  resembling  nuclein. 


2IO  HISTOLOGY. 

enter  at  the  hilus,  divide  in  the  medulla,  and  are  characterized  by  their  tortuous 
course  (Fig.  194).  From  the  medulla  they  pass  to  the  cortex,  where  they  are 
principally  distributed  to  the  Graafian  follicles  in  which  they  form  capillary  net- 
works in  the  tunica  propria.  The  veins  form  a  dense  plexus  at  the  hilus  of 
the  ovary.  The  lymph-vessels  are  numerous,  and  may  be  traced  to  the  tunica 
propria  of  the  follicles.  Medullated  and  nonmedullated  nerves  in  large  num- 
bers enter  at  the  hilus  in  company  with  the  blood-vessels,  to  the  walls  of  which 
the  majority  of  them  are  distributed.  A  few  of  the  nerves  proceed  to  the 
cortex  ;  these  form  a  dense  plexus  of  delicate,  mostly  gray  fibers,  which  em- 
braces the  follicles  and  sends  minute  fibrils  to  the  walls  of  the  blood-vessels 
and  (in  the  cat)  between  the  epithelial  cells  of  the  larger  follicles. 

The  cpoophoron  ox  parovarium  and  Xht paroophoron  are  embryonal  remains. 
The  former  lies  within  the  broad  ligament  between  the  ovary  and  oviduct  and 
consists  of  a  group  of  convoluted  blind  tubules,  lined  with  ciliated  columnar 
epithelium.  The  parovarium  is  the  remdins  of  the  middle  or  sexual  segment  of 
the  Wolffian  body.  The  paroophoron  consists  of  branched  tubules  lined  with 
ciliated  columnar  epithelium,  and  is  embedded  in  the  broad  ligament  between 
the  ovary  and  uterus  ;   it  represents  the  posterior  segment  of  the  Wolffian  body. 

THE  OVIDUCT. 

The  walls  of  the  oviduct  or  Fallopian  tube  consist  of  three  coats  :  an 
inner  mucous,  a  middle  muscular,  and  an  outer  serous.  The  tnucous  membrane  is 
thrown  into  numerous  longitudinal  folds,  so  that  on  tranverse  section  the  lumen 
of  the  narrow  portion  of  the  oviduct  has  a  stellate  outline.  The  folds  corre- 
spond in  amplitude  to  the  size  of  the  tube  and  are  highest  in  the  ampulla, 
where  they  are  united  to  one  another  by  minute  oblique  secondary  plications. 
The  thick  mucous  coat  is  composed  of  a  fibro-elastic  tunica  propria  con- 
taining numerous  connective-tissue  cells,  and  of  a  layer  of  simple  ciliated 
columnar  epithelium  ;  the  ciliary  wave  is  directed  toward  the  uterus.  Outside 
of  the  tunica  propria  is  an  extremely  thin  muscularis  mucosae  consisting  of 
longitudinally-disposed  bundles  of  smooth  muscle-fibers.  The  submucosa  is 
represented  by  a  thin  layer  of  fibrillar  connective-tissue.  The  muscular  coat 
consists  of  an  inner  thicker  circular  and  an  outer  very  thin  longitudinal  layer 
of  involuntary  muscle-fibers.  The  serous  tunic  is  formed  by  the  peritoneum 
and  a  considerable  layer  of  loosely-united  connective-tissue  bundles. 

The  blood-vessels  are  especially  abundant  in  the  mucosa,  where  they  form 
a  narrow-meshed  capillary  network.  The  larger  veins  run  along  the  bases  of 
the  longitudinal  folds  of  the  mucosa.  The  knowledge  of  the  relations  of  the 
lymph-vessels  and  the  ultimate  distribution  of  the  nerves  is  still  imperfect. 

THE  UTERUS.* 
The  walls  of  the  uterus,  like  those  of  the  oviduct,  consist  of  a  mucosa,  a 
muscularis,  and  a  serosa. 

*  This  chapter  has  been  revised  and  considerably  enlarged  by  the  editor. 


THE  FEMALE  REPRODUCTIVE  ORGANS.  211 

The  serosa  exhibits  no  special  characteristics. 

The  mtiscularis  consists  of  smooth  nniscle-fibers,  united  into  bundles 
which  interlace  in  all  directions,  so  that  a  .sharp  demarcation  of  single 
layers  is  not  possible ;  still,  in  general,  three  strata,  more  or  less  well-defined, 
may  be  distinguished:  (i)  an  inner  layer  (stratum  submucosum),  composed 
chiefly  of  bundles  disposed  in  a  longitudinal  direction;  (2)  a  middle  layer, 
the  most  robust,  consisting  of  bundles  having  in  general  a  circular  dis- 
position, and  containing  the  principal  ramifications  of  the  arteries  and  also  a 
well-developed  venous  plexus,  hence  the  name  stratum  vasculare ;  (3)  and  an 
outer  layer  (stratum  supravasculare),  formed  partly  of  bundles  extending  in  a 
circular,  partly  in  a  longitudinal  direction,  the  latter  close  beneath  the  serosa, 
with  which  it  is  intimately  united.  The  stratification  of  the  muscular  tissue  is 
more  pronounced  in  tlie  cervix,  where  an  inner  and  an  outer  longitudinal  may 


;.  199.— From  a  Transverse  Section  of  thb  Middle  op  the  Uterus  op  a  Girl  Fifteen  Years  Old. 
X  10.  a.  Epithelium;  ^,  tunica  propria  ;  c,  glands  ;  i,  inner  muscular  layer  (stratum  submucosum) ;  2,  mid- 
dle muscular  layer  (stratum  vasculare) ;  3,  outer  muscular  layer  (stratum  supravasculare).    Techn.  No.  153. 


be  distinguished  from  a  middle  circular  layer.  The  volume  of  the  muscularis 
is  subject  to  great  variation,  dependent  on  the  functional  condition  of  the 
uterus. 

Tlie  miiscle-Jihers  differ  somewhat  from  the  elements  of  smooth  muscle- 
tissue  as  found  in  other  organs.  They  are  elongated  cells,  usually  spindle- 
shaped,  or  are  blunted  and  frayed  at  the  ends.  Frequently  they  are  forked  at 
their  extremities.  Their  length  varies  greatly ;  in  the  virgin  uterus  from  40 
to  60  !x ;  during  pregnancy  they  increase  excessively,  and  at  the  end  of  the 
same  attain  a  size  of  from  300  to  600  /i.  The  nucleus  (not  infrequently  two 
or  more  are  present  in  one  cell)  is  usually  oval,  and  lies  embedded  in  a  granu- 
lar substance. 


212  HISTOLOGY. 

The  mucosa  is  sharply  defined  from  the  muscularis.  It  is  the  coat  which 
in  the  different  functional  conditions  of  the  uterus  undergoes  the  profoundest, 
and  physiologically  the  most  important  changes.  A  description  of  the  histo- 
logic structure  of  the  mucosa  of  the  uterus  can,  therefore,  only  answer  to  the 
corresponding  functional  condition  of  the  organ,  and  in  consideration  hereof 
will  be  presented  in  separate  sections. 

It  is  desirable  to  consider  : — 

1.  The  mucosa  of  the  virgin  resting  organ. 

2.  The  muco.sa  of  the  menstruating  uterus. 
^.   The  mucosa  of  the  erravid  uterus. 


j» 


-     --    Gland-lubule. 


L 


,  Utekvs  of  a 
Davidoff.) 


X  li-(A/ter  Boh» 


The  mucosa  of  the  virgin  resting  uterus  (Fig.  200),  after  the  advent  of 
puberty,  has  a  thickness  of  from  i  to  2  mm.  and  bears  on  its  surface  a  single 
layer  of  ciliated  columnar  epithelium,  30 /j.  in  height  in  the  middle  regions ; 
the  ciliary  wave  is  directed  toward  the  cervix.  The  tunica  propria  is  formed 
of  a  fine  fibrous  tissue  closely  resembling  embryonal  connective  tissue ;  it  con- 
sists of  elongated  cells  furnished  with  oval  nuclei,  which  send  out  in  all  direc- 
tions branched  processes  which  unite  with  those  of  neighboring  cells  and 
form  a  cellular  network,  the  meshes  of  which  are  occupied  by  lymph  and 
numerous  leucocytes. 

The  tunica  propria  supports  many  simple  or  forked  gland-tubules,  the 
upper  part  of  which  pursues  a  course  more  or  less  vertical  to  the  surface  of  the 


THE    KE.MAI.F.    REPRODl'CTIVE    ORGANS. 


213 


mucosa,  while  the  lower  half  usually  appears  irregularly  spiral.  The  glands 
extend  clo.se  up  to  the  muscularis,  and  here  not  infrequently  they  are  bent  at 
right  angles,  so  that  the  fundus  runs  parallel  to  the  muscular  coat.  The  glands 
of  the  uterus  are  to  be  regarded  as  invaginations  of  the  superficial  epithelium, 
and  consist  likewise  of  a  simple  layer  of  ciliated  epithelium  resting  upon  a 
delicate  basement  membrane  composed  of  anastomosing  connective-tissue  cells. 
The  blood-vessels  run  in  a  winding  manner  from  the  muscularis  to  the 
surface  of  the  muco.sa,  and  the  arteries,  especially,  are  characterized  by  their 
extremely  convoluted,  corkscrew-like  course.  At  the  surface  they  break  up  into 
capillaries  and  form  a  clo.se  network.     A  similar  network  surrounds  the  gland- 


ds..^^;>.r, 


"  Superficial  epithelii 


Excretory  duct. ---j 


Fig.  aoi.— Mucous  .Memdranb  op  a  Vikgi 
integrating  surf:ice ;  pd,  pit-like  depress! 
larged.     X  3=  —{Schafier.) 


Utbrus  During  thr  First  Day  op  Mbnstruation.    ds.  Dis- 
1  of  the  mucous  membrane ;  gl,  glandular  lumen  very  much  en- 


tubules.  The  veins  ])roceeding  from  the  capillaries  form  a  plexus  in  the  deeper 
strata  of  the  muccsa,  that  is  especially  well  developed  in  the  cervix  and  par- 
ticularly around  the  external  orifice. 

In  the  cen'ix  the  mucous  membrane  is  thicker,  and  in  its  upper  two-thirds 
is  clothed  with  a  single  layer  of  tall  ciliated  cells  (60  .a  high  in  the  middle  por- 
tion),* while  toward  the  external  orifice  papilla;  covered  by  a  stratified  squam- 
ous epithelium  appear.  In  addition  to  a  few  scattered  tubular  glands,  mucous 
follicles,  the  so-called  mucous  crypts,  occur;    they  are   i   mm.   wide,  possess 


*  Transformation  of  these  cells  into  goblet-cells  occurs. 


214 


HISTOLOGY. 


many  evaginations,  and  by  retention  of  their  secretion  are  converted  into  cysts, 
the  ovula  Nabothi. 

During  the  period  of  iiicnstniation  a  number  of  progressive  and  retrogres- 
sive changes  take  place  in  the  mucosa  of  the  uterus,  which  may  be  grouped  in 
three  phases : — 

((?)  Thickening  of  the  mucosa,  accompanied  by  changes  in  its  histologic 
structure. 

(iJ)   Menstruation  proper. 

(;:)   Regeneration. 

The  initial  phase  is  characterized  by  a  considerable  increase  in  the  thick- 
ness of  the  mucosa   (up  to   6   mm.),   in  consequence  of  which  the  surface 


Excretory  duct. 


Cavernous  layer.  ^ 


-"  Gland'tubiiles. 


becomes  irregular  and  the  orifices  of  the  glands  ojien  in  deep  depres- 
sions. The  thickening  of  the  mucosa  depends  in  a  measure  on  an  actual 
increase  of  the  tissue,  produced  by  proliferation  of  the  connective-tissue  cells 
and  leucocytes  and  by  growth  of  the  gland-tubules,  which  in  the  process 
take  up  an  irregular  course  and  become  essentially  wider.  Simultaneously  the 
blood-vessels,  especially  the  veins  and  capillaries,  undergo  enormous  disten- 
tion, whereby  the  blood-supply  of  the  organ  is  extraordinarily  augmented.  In 
this  condition  the  mucosa  is  designated  decidiia  menstrua  lis. 

These  changes  are  followed  by  a  partial  disintegration  of  the  superficial 
strata  of  the  mucosa,  accompanied  by  an  infiltration  of  blood  into  the  sub- 
epithelial tissues.     The  molecular  disintegration  (associated  with  fatty  degen- 


THE  FEMALE  REPRODUCTIVE  ORGANS. 


215 


eration)  of  the  surface  advances  rapidly,  the  greath'-dilated  superficial  blood- 
vessels become  exposed,  rupture,  and  cause  hemorrhages  within  the  uterine  cavity, 
which  flow  into  the  vagina  and  give  rise  to  the  external  phenomena  of  men- 
struation. After  this  discharge  of  blood  the  mucosa  becomes  rapidly  reduced  in 
thickness.  The  surface  is  now  entirely  devoid  of  epithelium,  and  consists  of  con- 
nective tissue  and  exposed  blood-vessels.  This  condition  is  immediately  suc- 
ceeded by  the  stage  of  regeneration.  The  hyperemia  disappears  rapidly,  the 
extravasated  blood  is  partly  resorbed,  partly  cast  off,  a  cellular  network 
grows  upward  and  restores  the  lost  tunica  propria,  while  from  the  gland-cells  the 
epithelial  covering  of  the  mucosa  is  regenerated.  New  subepithelial  capil- 
laries are  formed. 

The   histology  of  the   mucosa  of  the  uterus  during  pregnancy  (decidua 
graviditatis)  (Fig.  202  and  Fig.  203)  is,  on  the  whole,  like  that  of  the  decidua 


Fig.  203. — Vertical  Sbction  thkough  the  Wall 
THE  Fetal  Membranes  i.s  Situ.  Between  il 
gelatinous  connective  tissue.     X  y>. — {.Schajter.) 

menstrualis,  with  the  alterations  more  pronounced.  It,  however,  undergoes 
considerable  modification  because  of  its  intimate  relations  with  the  developing 
ovum  in  the  uterus.  These  relations  vary,  and  thus  in  the  course  of  develop- 
ment three  essentially  different  parts  of  the  mucosa  may  be  distinguished  : — 

((r)  The  Jecidiia  serotina  (decidua  basalis),  the  area  of  the  mucosa  to 
which  the  ovum  is  attached  (placenta  uterina). 

(/')  The  decidua  vera,  which  comprises  all  the  remaining  portion  of  the 
mucosa  attached  to  the  wall  of  the  uterus. 

(c)  The  decidua  reflexa  (decidua  capsularis),  the  portion  of  the  mucosa 
which  ])rojects  into  the  cavity  of  the  uterus  and  encapsules  the  ovum. 

The  decidua  .serotina  and  vera  undergo  progressive  development  during 
the  entire  course  of  jiregnancy  and  ]iersist  until  its  close  ;  the  decidua  reflexa 
becomes  graduallv  attenuated  and  disapiiears  in  the  course  of  the  fifth  month. 


2l6  HISTOLOGY. 

A  section  of  the  greatly  thickened  mucosa  (decidua  vera  and  serotina) 
shows  the  same  histologic  details  that  have  been  described  in  the  menstrual 
decidua,  but  with  this  difference,  that  the  progressive  alterations  (proliferation 
of  the  connective-tissue  elements,  distention  of  the  blood-vessels  and  glands) 
attain  much  greater  proportions.  A  superficial  compact  zone  and  a  deep  spongy 
zone  can  always  be  distinguished  (Fig.  202).  The  cavities  in  the  latter  are 
produced  by  the  lower  divisions  of  the  gland -tubules,  which  have  become 
greatly  widened  and  very  tortuous.  At  a  later  stage  of  pregnancy,  owing  to  the 
great  distention  of  the  uterus,  the  lumina  of  the  glands  appear  compressed  and 
straighter  (parallel  to  the  muscular  coat)  (Fig.  203).  Between  the  glands  are 
numerous  blood-vessels,  spindle-cells,  and  multinucleated  giant-cells.  The 
epithelium  of  the  glands  begins  early  to  loosen,  and  in  great  part  the  cells  lie 
irregularly  scattered  in  the  lumen  of  the  tubule,  where  they  disintegrate.  The 
orifices  of  the  glands  are  gradually  obliterated,  since 
\  ^^  the  walls,  after  the  loss  of  the  epithelium,  become 

adherent  and  grow  together. 

The  blood-vessels  of  the  mucosa  are  all  dilated, 
especially  the  superficial  veins  and  capillaries ;  the 
latter  often  form  distended  sinus-like  cavities  in  the 
upper  layer  of  the  decidua.  In  the  decidua  serotina 
the  arteries  and  veins  open  on  the  surface  of  the 
mucosa  (Fig.  205  and  Fig.  206),  so  that  here  the 
maternal  blood  circulates  between  the  chorionic  villi 
of  the  placenta  (see  Placenta,  page  217).  In  the 
decidua  vera  the  blood-vessels,  toward  the  end  of 
pregnancy,  are  less  conspicuous. 

Of  especial  interest  are  peculiar,  typical  cells, 
decidual  cells,  which  appear  in  large  numbers  in  the 
mucosa  of  the  gravid  uterus.      They  are  flattened, 
spherical,  oval,  or  branched  cells  of  conspicuous  size 
(0.03  to  o.  I  mm.),  which,  in  the  latter  half  of  pregnancy,  assume  a  characteris- 
tic brown  color.      They  possess  usually  but  one  nucleus,  though  occasionally 
two,  three,  or  more  are  present,  and  in  rare  cases  as  many  as  30  or  40. 

The  decidual  cells  are  most  numerous  and  most  densely  aggregated  in  the 
upper  compact  zone  of  the  serotina  (Fig.  203),  which  owes  its  typical  character 
and  brown  color  to  these  elements.  Occasionally  cells  are  found  that  are  united 
with  one  another  by  means  of  protoplasmic  processes.  According  to  Minot, 
the  decidual  cells  originate  from  connective-tissue  elements,  and  therefore  may 
be  regarded  as  a  modified  embryonal  or  so-called  anastomosing  connective  tis- 
sue. 

In  a  cross-section  of  the  decidua  vera,  in  the  latter  half  of  pregnancy,  it 
will  be  seen  that  the  surface  of  the  mucosa  is  covered  by  two  distinct  mem- 
branes— fetal  membranes — the  chorion  and  the  amnion  (Fig.  203).  The  cho- 
rion lies  next  to  the  decidua  vera,  and  is  intimately  united  with  it.  It  consists 
of  two  layers,  an  epithelial  and  a  connective-tissue  layer,  of  which  the  former  is 


Fig.    204. — Oi 

ECIDUAL 

Crlls 

FROM      THE 

Mucous     Mhm- 

BRANB      OF 

HUMAN 

Utbrus 

ABOUT  SEVE^ 

1   MoNTf 

[S  Prbg- 

NANT.     Belo' 

IV  a  "gia 

Lnt-cell," 

above  to  the 

right  a 

cell  with 

akaryokincti 

c  figure. 

X  250  — 

(Sdu.per.) 

THE  FEMALE  REPRODUCTIVE  ORGANS.  217 

turned  toward  the  uterine  wall,  the  latter  toward  the  amnion.  Two  similar 
layers  may  be  distinguished  in  the  amnion,  but  of  these  the  epithelial  layer, 
which  consists  of  cubical  cells,  is  turned  toward  the  cavity  of  the  uterus,  while 
the  connective-tissue  stratum  faces  the  chorion.  The  amnion  and  chorion  are 
loosely  united  to  each  other  by  mucous  connective  tissue,  in  which  delicate 
fibrils  may  be  .seen  extending  from  one  membrane  to  the  other. 

The  /vmph-vesse/s  of  the  uterus  form  in  the  mucosa  a  wide-meshed  network 
])rovided  with  blind  branches.  From  this  small  stems  proceed  through  the 
muscularis,  and  communicate  with  a  close  subserous  network  of  larger  chan- 
nels. 

The  nerves  of  the  uterus,  medullated  as  well  as  nonmedullated,  are  very 
numerous.  They  branch — the  medullated  nerves  after  losing  their  medullary 
sheath — in  the  muscularis,  and  form  a  dense  ple-xus  in  this  and  in  the  mucosa. 
From  the  latter  delicate  fibrils  may  be  traced  between  the  epithelial  cells. 


THE   I'L.VCKNTA.* 

The  placenta  is  an  organ  which  from  a  morphologic  standpoint  is  com- 
])o.sed  of  two  heterogeneous  parts,  of  which  the  one  is  produced  by  the  mother 
(placenta  uterina ),  the  other  by  the  embryo  (placenta  foetalis).  It  is  the  result 
of  the  intimate  union  of  a  circumscribed  area  of  the  chorion  (chorion  fron- 
dosum),  with  that  portion  of  the  mucosa  of  the  uterus  known  as  the  decidua 
serotina.  The  placenta  serves  the  purpose  of  bringing  the  fetal  and  maternal 
blood  into  the  closest  proximity,  to  render  possible  the  interchange  of  materials 
between  them.  To  subserve  this  function  the  organ  possesses  a  peculiar 
histologic  construction,  in  which  the  blood-vessels,  especially  in  their  arrange- 
ment and  structure,  take  a  i)rominent  part. 

In  the  histologic  investigation  of  the  placenta  various  obstacles  are 
encountered,  owing  to  its  being  an  extremely  soft  spongy  mass,  traversed  by 
numerous  wide  blood-vessels.  The  comprehension  of  the  minute  structure  will 
be  considerably  facilitated  by  proceeding  from  the  previously-mentioned  fact 
that  the  finished  organ  is  the  product  of  two  originally  heterogeneous  struc- 
tures, the  chorion  on  the  one  side,  the  decidua  serotina  on  the  other,  and  that 
this  union  is  substantially  effected  in  that  the  chorion,  by  means  of  numerous 
villous-like  proliferations,  penetrates  the  underlyitig  serotina,  the  surface  of  which 
is  peculiarly  modified  and  fiirther  regressively  altered  for  its  reception,  and  as  it 
were  takes  root  in  the  same.  For  the  investigation  of  these  relations  sections 
through  the  wall  of  the  uterus  with  the  placenta  in  situ,  toward  the  end  of 
pregnancy,  are  most  instructive.  In  such  a  section  two  sharply-defined  zones 
may  be  recognized  :  an  outer  compact  stratum  consisting  of  the  greatly-thickened 
muscular  coat  of  the  uterus,  covered  externally  by  the  serosa,  and  an  inner  spongy 
zone  containing  numerous  inter-communicating  spaces  filled  with  blood.  The 
latter  is  the  placenta ;  that  is,  the  united  decidua  serotina  and  chorion  frondosum. 

*This  chapter  is  an  entirely  new  addition  liy  the  editor. 


v"°^i,'-'""  A?~'^^ 


Ve 


Fig.  205. — Section  through  a  Normal  Human  Placenta  of  about  Sevb 
nion  :  Cho,  Chorion;  Vi,  villus  trunk;  vi,  sections  of  villi  in  the  substan. 
basalis;  Mc,  muscularis  ;  D',  compact  layer  of  decidua  ;  Ve,  uterine  artery 
fetal  blood-vessels  are  drawn  black  :  the  maternal  blood-spaces  are  left  whit' 
xcept  the  canalized  fibrin,  which  is  shaded  by  lines ;  the  remnants  of  the  | 


dark.— (^/j'^r  Mitwt.) 


N  Month 

s 

N  Situ 

Am 

.  Am- 

ce  of  the 

p'l 

icenta ■ 

D,  d 

:cidua 

opening  i 

nto 

the  plk 

ceiUa. 

The 

e  ;  the  cho 

rio 

nic  tissu 

e  is  St 

ppled 

gland  cav 

tie 

5  in  D" 

are  st 

ppled 

218 


THE    1-EMAI.F,    REPRODUCTIVE    ORGANS. 


219 


The  accompanying  illustration  (Fig.  205)  shows  their  relations  under  low  mag- 
nification, which  will  be  elucidated  by  referring  to  the  schematic  representation 
in  Fig.  206. 

The  surface  of  the  placenta  directed  toward  the  cavity  of  the  uterus  is 
covered  by  a  compact  stratum,  X\\Qmeml>rana  choiii,  which  is  composed  chiefly 
of  fibrillar  connective  tissue,  and  in  which  the  main  branches  of  the  umbilical 
blood-vessels  run.  The  outer  surface  of  the  chorion  is  covered  by  a  delicate 
membrane,  the  placental  portion  of  the  amnion,  which,  as  previously  stated, 
consists  of  an  inner  epithelial  and  a  connective-tissue  layer,  and  is  con- 
nected with  the  chorion  by  means  of  embryonicconnective  tissue.  The  other  sur- 
face of  the  membranachorii,  that  directed  toward  the  wall  of  the  uterus,  is  closely 
beset  with  innumerable  villous-like  structures,  large  and  small,  which  in  the 


Chorionic  villi. 


Intervillous  spaces. 


"^^'TnO-O^A^^^-^  no.in.v 


Attached  villi. 


Spiral  artery. 
Gland. 


upper  part  of  the  placenta  form  a  dense  tangle,  and  whose  terminal  ramifica- 
tions are  embedded  in  the  cleft,  uneven  substance  of  the  serotina.  On  closer 
study  of  this  villous  tangle  it  will  be  seen  that  the  larger  stems  run  a  more  or 
less  direct  course  from  the  chorion  to  the  serotina,  in  order  to  secure  a  firm 
union  with  the  latter,  while  their  many  much-branched  lateral  twigs  usually 
establish  no  connection  with  the  uterine  portion  of  the  placenta,  but  terminate 
free  in  the  blood-spaces,  the  so-called  iiiterfillous  spaces,  between  the  chorion 
and  serotina.  Dependent  upon  these  relations  the  branches  of  the  chorionic 
villi  are  divided  into  "  roots  of  attachment"  or  main  stems,  and  free  processes  or 
floathh:;  villi.  From  the  chorion  a  branch  of  the  umbilical  artery  enters  each 
main  stalk  and,  within  the  terminal  ramifications  of  the  villus,  breaks  up  into 
a  dense  capillary  network  from  which  the  umbilical  veins  take  their  origin  and 
carry  hack   the  blood    from   the   chorion   through   the   umbilical  cord   to  the 


2  20  HISTOLOGY. 

fetus.      Accordingly,  the  blood-vessel  system  of  the  fetal  placenta  is  entirely  closed. 
Notuhei-e  does  a  direct  intermingling  of  maternal  and  fetal  blood  occur. 

A  cross-section  of  one  of  the  smaller  chorionic  villi,  highly  magnified, 
shows  that  it  is  chiefly  composed  of  mesenchymal  tissue  (mucous  tissue),  in 
which  the  blood-vessels  are  embedded  (Fig.  207).  This  central  supporting 
substance  is  covered  by  an  irregular  and  not  everywhere  continuous  stratum  of 
epithelium.  In  the  earlier  months  of  development  two  distinct  strata  may  be 
distinguished  in  the  epithelium  of  the  villi :  an  inner,  lying  immediately  upon 
the  supporting  tissue,  in  which  the  cells  possess  large  nuclei  and  definite  contours, 
so  that  in  the  main  they  are  distinctly  separated  from  one  another  ;  and  an  outer 
layer,  consisting  of  a  continuous  protoplasmic  mass — syncytium — containing 
numerous  small  irregularly-scattered  nuclei.  Toward  the  end  of  pregnancy, 
however,  the  epithelium  of  the  villi  undergoes  great  alteration,  as  appears  in  the 


Protopl: 

Epithelial  nucleus. , 

Capillaries  *'-''l^ 


Cell-patch  (Zeilkncten)    - 


'1V''«*».^    __»/  Capillarv. 


Cell- patch  (Zellknoten). 


:  (.A)  AND  Lakgek  IB)  Chokionic  Vi: 
Precnanlv.     X  2io.—{Scha/€r.) 


illustration  (Fig.  207).  On  the  larger  villi  a  true  epithelial  investment  has 
almost  entirely  disappeared  and  instead,  isolated  accumulations  of  large  round 
nuclei  are  found  ;  they  stain  intensely,  are  embedded  in  a  clear,  homogeneous 
substance,  and  form  protuberances  {Zellknoten,  cell-patches')  on  the  surface  of 
the  villi.  Between  these  cell-patches  the  connective  tissue  of  the  villi  is  fre- 
quently covered  only  by  a  thin,  homogeneous  stratum,  or  in  other  cases  (espe- 
cially in  smaller  villi)  this  stratum  still  retains  more  or  less  the  character  of 
the  protoplasm  containing  scattered  nuclei.  There  are  many  indications  that 
the  latter  is  the  remains  of  the  syncytium,  while  the  cell-patches  probably 
originated  in  the  primitive  inner  stratum  of  the  epithelium  of  the  villi.  In 
many  places  the  syncytium  becomes  transformed  into  a  peculiar  hyaline  sub- 
stance, permeated  by  fissures,  which  often  lies  upon  the  chorion  in  dense  strata, 
and  is  called  canalized  fibrin.* 


*  It  has  not  been  as  yet  determined  with  certainty  whether  the  epithelium  of  the  villi  of 
the  human  placenta  is  derived  entirely  from  the  epithelium  of  the  chorion,  or  whether  the  epithe- 


THE  FEMALE  REPRODUCTIVE  ORGANS.  221 

The  histologic  structure  of  the  maternal  portion  of  the  placenta — placenta 
uten'iia — in  its  essential  features  has  been  described  in  connection  with  the 
decidua  in  the  preceding  chapter.  Certain  peculiarities,  however,  as  well  as 
the  union  of  the  maternal  and  fetal  placenta  in  a  functional  whole  require  a 
brief  consideration. 

The  placental  portion  of  the  decidua  (Fig.  205),  that  forming  the  lower 
stratum  of  the  placenta  (basal-plate),  becomes  greatly  thinned  (0.5  to  i.o  mm.), 
however,  as  in  the  e.\traplacental  portion,  an  upper  compact  layer,  and  a  lower 
cavernous  layer  (gland  lumina)  may  be  distinguished.  The  decidual  cells  are 
extremely  numerous  and  lie  closely  crowded.  .\  honeycombed  structure  of 
connective-tissue  septa  {septa placentce)  arises  from  the  surface  of  the  serotina, 
directed  toward  the  intervillous  spaces,  and  penetrates  between  the  villi  of  the 
chorion,  separating  the  latter  into  lobes  or  cotyledons.  Only  in  the  peripheral 
regions  of  the  placenta  do  these  septa  reach  to  the  membrana  chorii,  where 
frequently  they  form  on  the  inferior  surface  of  the  latter  a  thin  membranous 
stratum,  the  decidua  placentalis  siibchorialis.  On  the  margin  of  the  placenta 
the  serotina  gradually  increa.ses  in  thickness  and  pa.sses  into  the  vera,  at  which 
point  it  is  closely  applied  to,  and  firmly  united  with,  the  chorion.  Within 
the  area  of  the  placenta,  however,  the  chorion  and  serotina  are  far  apart,  and 
the  space  between  them  is  filled  with  the  above-described  chorial  villi  and 
the  blood  circulating  between  them  ;  it  is  maternal  blood  that  surrounds  the 
villi  on  all  sides,  and  is  thus  brought  into  the  closest  relation  with  the  fetal 
circulation. 

Of  especial  interest  is  the  behavior  of  the  blood-vessels  within  the  placenta 
uterina  (Fig.  205  and  Fig.  206).  Numerous  <z/-/m«  from  the  muscularisof  the 
uterus  penetrate  the  serotina,  in  which  they  make  cork-screw-like  tours,  in  the 
course  of  which  they  lose  their  muscular  coat  and  continue  as  wide  tubes  consist- 
ing alone  of  the  lining  endothelium.  Near  the  surface  of  the  decidua  they  usually 
bend  sharply  at  right  angles,  and  then  open  directly  into  the  intervillous  spaces  of 
the  placenta.*    Noiohere  do  the  arteries  hreak  up  into  capillaries.    The  veins  (like- 


lium  of  the  serotina  participates  in  its  composition.  Recent  investigations,  however,  as  well  as 
comparative  anatomical  facts,  indicate  that  only  the  inner  epithelial  stratum  of  the  villi  comes 
from  the  chorionic  epithelium,  while  the  syncytium  is  derived  directly  from  the  mucosa  of  the 
uterus,  the  epithelium  of  which,  on  the  ingrowth  of  the  chorial  villi,  becomes  closely  applied 
to,  and  hiends  with,  the  epithelium  of  the  latter. 

*  In  regard  to  the  relation  of  the  decidual  bloodvessels  to  the  intervillous  spaces  there  are 
two  conflicting  theories.  According  to  the  one,  the  intervillous  spaces  are  independent  clefts, 
without  proper  walls,  that  are  formed  in  the  course  of  development  between  the  fetal  and  maternal 
portions  of  the  placenta,  and  with  which  the  blood- vessels  opening  on  the  surface  of  the  decidua 
are  in  direct  communication.  .Accordingly  the  villi  of  the  chorion  are  in  direct  contact 
with  the  mnternal  blooti  circulating  in  these  spaces.  The  opposite  view  regards  the  blood- 
spaces  of  the  placenta  as  the  enormously-widened  capillaries  of  the  decidua,  which,  during  the 
mutual  process  of  intergrowth  between  the  placenta  uterina  and  placenta  fetalis,  the  developing 
villi  of  the  chorion  have  invaginated.  -According  to  this  the  blood-vessel  system  of  the  decidua 
is  closed  and  the  arteries  and  veins  communicate  through  a  system  of  capillary  l.icun;v  (the  in- 
tervillous spaces).     Further,  the  chorial  villi  are  not  directly  bathed  in  the  maternal  blood,  but 


wise  endothelial  tubes,  though  wider  than  the  arteries )  also  are  in  direct  com- 
munication with  the  placental  spaces;  they  enter  the  decidua  usually  under  a  very 
narrow  angle,  run  more  or  less  parallel  to  the  surface,  and  unite  in  the  deeper 
strata  in  a  wide  venous  plexus.  In  accordance  with  the  description  of  these 
conditions  of  the, vessels,  the  arteries  and  veins  within  theserotinacan  no  longer 
be  recognized  by  the  histologic  structure  of  their  walls,  but  can  only  be  dis- 
tinguished by  their  width  and  their  course.  The  arteries  are,  in  addition,  usually 
characterized  by  a  thin  homogeneous  enveloping  stratum  that  stains  intensely 
with  carmine,  and  in  which  a  few  scattered  nuclei  are  found.  This  peculiar 
layer  is  probably  a  product  of  the  degenerated  muscular  coat. 

THE  VAGIN.A.  AND  THE  GENITALIA. 

The  vagina  is  formed  by  a  mucous  membrane,  a  muscular  tunic,  and  a 
fibrous  coat. 

The  mucous  membrane  is  composed  of  a  stratified  scaly  epithelium  and  a 
tunica  propria  beset  with  papillae  ;  the  latter  is  built  up  of  small  interlacing 
bundles  of  connective  tissue  profusely  intermingled  with  elastic  fibers,  and 
contains  a  variable  quantity  of  leucocytes.  The  latter  occasionally  exist  in 
the  form  of  solitary  nodules ;  in  this  case,  in  these  localities  numerous  wander- 
ing leucocytes  are  found  in  the  epithelium.  The  mucosa  rests  on  a  submucosa 
consisting  of  loosely-united  connective-tissue  bundles  and  of  robust  elastic 
fibers.      Glands  are  absent  within  the  vaginal  mucous  membrane. 

The  muscular  coat  comprises  an  inner  circular  and  an  outer  longitudinal 
layer  of  smooth  muscle-fibers. 

The  oviX^x  fibrous  tunic  is  a  dense  connective-tissue  structure,  rich  in  elastic 
fibers. 

The  blood-  and  lymph-vessels  are  arranged  in  jjarallel  horizontal  networks 
in  the  submucosa  and  the  tunica  propria.  Between  the  bundles  of  the  muscular 
tunic  lies  a  close  network  of  wide  venous  channels.  The  nerves  form  a 
plexus  beset  with  many  small  ganglia  in  the  outer  fibrous  tunic. 

The  mucous  membrane  of  the  external  genitalia  in  the  vicinity  of  the 
clitoris  and  the  urethral  orifice  differs  from  the  vaginal  mucosa  in  the  possession 
of  numerous  mucous  glands,  0.5  to  3  mm.  in  size,  and  on  the  labia  minora  in 
the  presence  of  sebaceous  follicles  (without  hair-follicles)  0.2  to  2  mm.  in  size. 
The  clitoris  repeats  on  a  diminutive  scale  the  structure  of  the  penis  ;  end-bulbs 
and  tactile-corpuscles  occur  in  the  glans. 

The  glands  of  Bartholin  are  the  homologues  of  the  glands  of  Cowper  in 
the  male. 

are  separated  from  it  by  a  thin  stratum  of  cells,  the  c.ipillary  endothelium,  which  lies  directly 
upon  them.  Recent  investigations  of  Keibel  apparently  support  the  latter  view,  since  in  a  human 
placenta  in  an  early  stage  of  development  he  succeeded  in  tracing  the  endothelium  of  the  de- 
cidual blood-vessels  into  the  intervillous  spaces,  and  demonstrating  it  as  a  continuous  stratum  on 
the  surface  of  the  chorionic  villi.  It  is  possible  that  in  the  further  development  of  the  placenta 
this  endothelial  covering  undergoes  regressive  change,  so  that  in  later  stages  it  cannot,  as  a  rule, 
be  demonstrated. 


THE    SKIN    AND    ITS    APPENDAGES.  223 

The  labia  majora  are  folds  of  the  integument  and  possess  the  same  structure. 
The  acid   vaginal   secretion  contains  desquamated    scaly  epithelial  cells 
and  leucocytes,  and  not  infrequently  an  infusorium,  trichomonas  vaginalis. 


IX.  THE  SKIN  AND  ITS  APPENDAGES. 

The  skin  is  composed  principally  of  connective  tissue,  which  however  is 
nowhere  exposed,  but  is  protected  by  the  superficial  epithelium  with  which  it 
is  connected.  The  connective-tissue  portion  of  the  skin  is  called  the  corium, 
Jerma,  or  true  skin  ;  the  epithelial  portion,  the  epidermis  or  cuticle.  The  ap- 
pendages of  the  skin,  the  nails,  and  the  hairs,  as  well  as  the  glands  and  the 
hair-follicles  embedded  within  the  corium,  are  products  of  the  epidermis. 

THE  SKIN. 

The  surface  of  the  corium  is  marked  by  many  furrows,  which  intersect  and 
enclose  rectangular  or  lozenge-shaped  areas  or  run  parallel  between  minute 
ridges.  The  lozenge-shaped  areas  may  be  seen  on  the  surface  of  the  greater 
part  of  the  body,  while  the  ridges  are  confined  to  the  volar  surface  of  the  hand 
and  the  plantar  aspect  of  the  foot.  These  areas  and  ridges  are  beset  with  numer- 
ous conical  elevations,  the  papillse,  whose  number  and  size  vary  greatly  in 
different  regions.  They  are  largest  (up  to  0.2  mm.  high)  and  most  numerous 
on  the  palm  of  the  hand  and  on  the  sole  of  the  foot;  they  are  very  slightly 
developed  in  the  skin  of  the  face. 

The  corium  is  composed  chiefly  of  interlacing  fibrous  connective-tissue 
bundles,  mingled  with  elastic  fibers,  cellular  elements,  and  smooth  muscle- 
fibers.  In  the  superficial  strata  of  the  corium  the  fibrous  bundles  are 
delicate  and  are  united  in  a  dense  feltwork  ;  in  the  deeper  strata  they  are 
larger  and  form  a  coarse-meshed  network.  These  differences  have  led  to  the 
recognition  of  two  strata  in  the  corium :  a  superficial  stratum  beset  with 
papilla;,  stratum  papillare,  and  a  deep  stratum,  stratum  reticulare.  There  is 
no  sharp  demarcation  between  the  two  strata,  the  one  gradually  blending 
with  the  other  (Fig.  208).  The  stratum  reticulare  is  connected  with  an  under- 
lying network  of  loosely-united  bundles  of  fibrous  tissue,  the  wide  meshes  of 
which  contain  clusters  of  fat-cells  ;  this  is  the  stratum  subcutaneum.  Much 
adipose  tissue  in  the  interfascicular  spaces  of  this  stratum  leads  to  the  formation 
of  the  panniculus  adiposus.  The  tissue  of  the  subcutaneous  stratum  is  firmly 
or  loosely  united  with  the  fibrous  sheaths  of  the  muscles  or  with  the  periosteum 
of  the  bones.  The  elastic  fibers,  which  are  thin  in  the  stratum  papillare  and 
stout  in  the  stratum  reticulare,  form  networks  distributed  uniformly  throughout 
the  corium.  The  cells  include  spindle-shaped  and  plate-like  elements,  leuco- 
cytes and  fat-cells.     The  number  of  the  cellular  elements  is  extremely  variable. 


2  24  HISTOLOGY. 

The  muscle-fibers  belong  almost  exclusively  to  the  non-striped  variety,  and  the 
majority  are  attached  to  the  hair-follicles;  only  in  a  few  situations  are  they 
disposed  as  a  membrane  (tunica  dartos,  nipple).  Striated  muscle-fibers  occur 
in  the  skin  of  the  face,  where  they  radiate  from  the  mimetic  muscles. 

The  epidermis  consists  of  a  stratified  squamous  epithelium,  in  which 
at  least  two  sharply-defined  zones  may  be  distinguished  :  a  deep,  soft,  so-called 
mucous  zone,  rete  mucositm  (stratum  Malpighii),  which  fills  the  depressions 
between  the  papilla:  of  the  corium,  and  a  superficial  firm  zone,  the  stratum 
corncuin.  Both  strata  are  composed  exclusively  of  epithelial  cells,  which  vary 
in  appearance  in  the  different  layers.  In  the  deepest  layer  of  the  rete  muco- 
sum  the  cells  are  cylindrical  and  possess  oval  nuclei ;  these  are  followed  by  sev- 
eral layers  of  polyhedral  cells  beset  with  numerous  minute  spines — prickle- 


r  Stratum  papillare 
Coriiim.   '        Excretory  duct 


Stratutn  reticul; 


Stratum  subcutj 


v^ 


cells.  The  spines  are  delicate  thread-like  processes,  which  penetrate  the  inter- 
cellular cement-substance  and  unite  neighboring  cells  to  one  another.  In  the 
rete  mucosum  new  cells  are  continually  being  formed  by  indirect  division. 

The  stratum  corneum  is  not  everywhere  of  the  same  structure.  In  locali- 
ties where  the  epidermis  is  well  developed,  as  on  the  palm  of  the  hand  and  the 
sole  of  the  foot,  several  layers  of  cells  characterized  by  highly-refracting  granules 
— granules  of  eleidin — lie  at  the  inner  border  next  to  the  rete  mucosum.  The 
granules  of  eleidin,  or  keratohyaline  granules,  are  produced  by  the  cornifica- 
tion  of  parts  of  the  cell-protoplasm.*  These  layers  form  the  stratum  granulo- 
sum.      In  the  next  layer  the  granules  dissolve  and  blend  with  the  protoplasm 


*  These   granules  dissolve  in  a  solution   of  potassium  hydroxid   and,  therefore,  are  not 
composed  of  keratin,  which  is  insolulile  in  tliis  reagent. 


THE    SKIN    AND    ITS    APPENDAGES.  225 

not  yet  transformed  into  horny  substance,  and  form  a  uniformly  clear  zone,  the 
stratum  lucidiim.  This  is  covered  by  the  deep  stratum  corncum  proper.  In 
this  stratum  all  the  non-cornified  parts  of  the  cell,  under  the  influence  of  the 
atmosphere,  become  desiccated  ;  and  so  it  happens  that  each  cell  contains  a  deli- 
cate horny  mesh-work,  and — as  the  intercellular  bridges  also  become  cornified 
— is  enveloped  in  a  horny  membrane.  The  nucleus  desiccates  ;  the  space  which 
it  occupied  persists  for  a  long  period.  The  partl\  cornified,  partly  desiccated 
cells  are  only  slightly  flattened. 

In  situations  where  the  epidermis  is  thinner,  the  stratum  granulosum  is 
narrow  and  interrupted.  The  stratum  lucidum  is  wanting.  The  horny  cells  of 
the  stratum  corneum  become  e.\tremely  compressed  and  united  in  lamella;. 
The  last  trace  of  the  nucleus  disappears. 


Part  of  stratum  corncum. 

m^  Stratum  iucidum. 

\     '  -S  Stratum  granulosum. 


k     'ttlgMt\  '•■*       *    *   _      *«  *y P»"  of  papillary  layer 


•Va% 


1A* 


^r 


'i'he  surface  of  the  horny  stratum  undergoes  a  continual  physiologic  des- 
quamation ;  the  resulting  loss  is  compensated  by  the  pushing  upward  of  the 
growing  elements  of  the  rete  mucosum. 

The  color  of  the  skin  is  due  to  the  deposition  of  fine  granules  of  pigment 
between  and  within  the  cells  of  the  deeper  layers  of  the  epidermis  ;  only  in 
certain  localities,  for  example,  in  the  vicinity  of  the  anus,  are  pigmented  con- 
nective-tissue cells  found  in  the  adjacent  coriuni. 

With  regard  to  the  source  of  the  pigment  there  are  two  theories,  of  which 
the  one  attributes  its  production  to  the  connective  tissue,  the  other  to  the  epi- 
«S 


226 


HISTOLOGY. 


thelium.  According  to  the  first,  the  so-called  ''transportation"  theory,  the 
pigment  is  carried  to  the  epithelium  by  pigmented  connective-tissue  cells  that 
wander  from  the  corium  into  the  epidermis,  and  then  disintegrate.  In  the 
human  hair-bulb  pigmented  forms  presenting  great  diversity  in  outline  are 
found  between  the  epithelial  elements ;  some  of  these  figures  are  cells,  but  it 
has  not  been  demonstrated  with  certainty  that  they  are  connective-tissue  cells, 
others  are  not  cells,  but  intercellular  clefts  filled  with  pigment.  The  second 
theory  is  supported  by  the  developmental  history,  which  teaches  that  the  pig- 
ment originates  in  the  epithelium  without  the  intervention  of  connective-tissue 
cells.  The  pigment  of  the  retina  also  is  certainly  and  exclusively  of  epithelial 
origin. 

THE  NAILS. 
The  nails  are  horny  laminae  which  rest  upon  the  nail-bed,  a  special  modi- 
fication of  the  skin.     The  nail-bed  is  bounded  on  the  sides  by  the  nail-malls, 
a  pair  of  sloping  folds  with  the  descent  forward.     The  nail-bed  and  nail-wall 
embrace  a  furrow,  the  nail-groove,  in  which  the  lateral  borders  of  the  nail  are 


Bone  of  ihird 
phalanx. 

Fig.  2IO. — DoRSA 


F  A  Cross-Section  of  the  Third  Phalanx  of  Child.    X  I5-    The  ridges  of 
Lil-t>ed  appear  in  cross-seclion  like  papillae.    Techn.  No.  155. 


inserted.  The  posterior  border  of  the  nail,  the  nail-root,  rests  in  a  similar  but 
deeper  groove,  the  tnatrix,  in  which  the  principal  growth  of  the  nail  takes 
place.  (Some  authors  name  the  whole  nail-bed  matrix,  which  is  in  a  measure 
justified  by  the  growth  of  the  nail  in  thickness  which  occurs  here.) 

The  anterior  free  edge  of  the  nail  projects  over  the  nail-ridge,  a  small 
seam-like  prominence  at  the  distal  end  of  the  nail-bed. 

The  nail-bed  consists  of  corium  and  of  epidermis.  The  fibro-elastic 
bundles  of  the  corium  are  in  part  disposed  parallel  to  the  long  axis  of  the 
fingers,  in  part  vertically  from  the  periosteum  of  the  phalanx  to  the  surface. 
There  are  no  papilte  on  the  corium,  but  minute  longitudinal  ridges.  They 
begin  low  at  the  matrix,  increase  in  height  toward  the  front  of  the  nail,  and 
terminate  abruptly  at  the  point  where  the  latter  leaves  its  bed.  The  epithelium 
is  of  the  stratified  scaly  variety,  of  the  same  structure  as  that  of  the  rete  mu- 
cosum  of  the  epidermis.  It  covers  the  ridges  of  the  nail-bed,  fills  up  the  fur- 
rows between  them,  and  is  sharply  defined  from  the  substance  of  the  nail.  The 
matrix,  likewise,  consists  of  corium  and  epidermis:  the  corium  is  distinguished 


THE    SKIN    AND    ITS    APPENDAGES.  227 

by  its  tall  papillae,  the  stratified  scaly  epithelium  is  very  thick  and  is  not 
sharply  defined  from  the  nail-substance,  but  passes  gradually  into  the  latter. 
This  is  the  place  where  by  continual  division  of  the  epithelial  cells  the  material 
for  the  growth  of  the  nail  is  furnished.  The  extent  of  the  matri.x  is  indicated 
by  the  It/ nil /a,  a  white  convex  area,  visible  to  the  unaided  eye,  produced  by  the 
thick,  uniform  rete  mucosum.  The  nail-wall 3X\A  the  nail-fold  (the  margin  of 
the  groove  overhanging  the  root  of  the  nail)  exhibit  the  same  general  structure 
as  the  skin  ;  the  rete  mucosum  blends  gradually  with  the  epithelium  of  the  nail- 
bed,  while  the  horny  stratum  extends  into  the  nail-groove  and  as  "  epony- 
chium  "  covers  a  small  portion  of  the  edge  of  the  nail,  but  soon  diminishes  in 
thickness  and  disappears  (Fig.  210). 

The  «<7// itself  consists  of  horny  epithelial  scales,  very  firmly  united  with 
one  another, which  possess  a  nucleus  and  differ  in  this  respect  from  the  horny 
cells  of  the  stratum  corneum  of  the  epidermis  (Fig.  211). 


THE  HAIR. 

The  hairs  are  flexible,  elastic  horny  threads,  which  are  distributed  over 
nearly  the  entire  surface  of  the  body  and  on  the  integument  of  the  cranium  are 
united  in  small  groups.  The  part  of  the  hair  which  pro- 
jects beyond  the  free  surface  of  the  skin  is  called  the 
shaft;  the  portion  obliquely  embedded  within  the  in- 
tegument, the  root;  at  its  lower  extremity  the  latter 
terminates  in  a  bulbous  expansion,  the  hair-bulb,  which 
embraces  a  formation  of  the  corium,  the  hair-papilla  (Fig. 
212). 

Each  hair-root  is  inserted  in  the  hair-follicle,  a  modi-  ^^^  211 -Elembhtsop 
fication  of  the  skin  in  the  formation  of  which  both  corium  T«:hn''No*'i'' 6  ^ '^°' 
and  epidermis  participate  ;  the  parts  furnished  by  the  latter 
are  the  epithelial  root-sheaths,  the  portion  originating  from  the  corium  is  the 
dermal  or  fibrous  sheath.  Into  the  follicle,  laterally,  two  to  five  glands  open, 
the  sebaceous  glands.  Bundles  of  smooth  muscle-fibers,  the  arrectores  pilorum, 
pass  obliquely  from  the  upper  surface  of  the  corium  and  attach  themselves 
to  the  fibrous  sheath  of  the  hair-follicle,  beneath  the  .sebaceous  glands ;  the 
point  of  insertion  of  these  fibers  is  always  on  the  side  toward  which  the  hair 
inclines  ;  when  they  contract,  the  follicle  and  the  shaft  become  erect. 

The  hair  consists  entirely  of  epithelial  cells,  arranged  in  three  well-defined 
strata  :  the  cuticle,  which  covers  the  surface  ;  the  cortical  substance,  which 
contributes  the  chief  bulk  ;  the  medulla,  which  occupies  the  axis  of  the  hair. 

The  cuticle  consists  of  a  single  layer  of  transparent  imbricated  scales — 
horny  epithelial  cells  without  nuclei. 

The  cortical  substance  of  the  shaft  consists  of  elongated  horny  epithelial 
cells  with  attenuated  nuclei,  which  are  intimately  united  with  one  another  ;  on 
the  root  the  cells  become  softer  and  rounder,  their  nucleus  correspondingly 
more  spherical,  as  they  approach  the  hair-bulb. 


2  28  HISTOLOGY. 

The  incchtlla  is  absent  in  many  hairs  ;  when  it  is  present  it  does  not  extend 
through  the  entire  length  of  the  hair.  It  consists  of  cubical,  finely-granular 
epithelial  cells,  which  contain  a  nidimentary  nucleus  and  are  usually  disposed 
in  twofold  rows. 

The  colored  hairs  contain  pigment,  diffused  and  in  the  form  of  granules, 
which  occurs  in  part  between  and  in  part  within  the  cells  of  the  cortical  sub- 
stance. In  every  hair  which  has  attained  its  full  development  minute  air- 
vesicles  occur;  they  are  found  in  the  cortical  substance  as  well  as  in  the 
medulla,  and  also  in  the  intercellular  clefts. 

The  follicle  of  fine  (lanugo)  hairs  is  formed  alone  by  the  epidermal  root- 
sheaths,  but  in  coarser  hairs  the  corium  participates  in  its  construction.  In  the 
follicles  of  the  latter  the  following  strata  may  be  distinguished  :    an  outer  loiii^i- 


Fat-cclls 
Fig.  212. — From  a  Thick  Cross-Section  i 


Techn.  No.  160. 


tiidinal  stratum  formed  of  loosely-united,  longitudinally-disposed  bundles  of 
white  fibrous  tissue,  mingled  with  elastic  fibers  and  richly  supplied  with  blood- 
vessels and  nerves  ;  a  middle  circular  stratum,  thicker,  and  consisting  of  small 
fibrous  bundles  circularly  arranged  ;  and  an  inner  clear,  homogeneous,  narrow 
belt,  the  glassy  or  hyaline  membrane,  resembling  in  character  the  elastic  mem- 
branes. Elastic  fibers  do  not  occur  in  the  middle  layer  nor  in  the  papilla. 
These  three  strata  are  derived  from  the  corium  and  together  constitute  the  der- 
mal <y!  fibrous  sheath  of  the  follicle.  Within  the  hyaline  membrane  lies  the 
outer  root-sheath  ;  it  is  a  continuation  of  the  rete  mucosum  of  the  epidermis  and 
consists  of  stratified  scaly  epithelium  ;  inward  to  this  lie  continuations  of  the 
stratum  corneum  and  stratum  granulosum,  which  extend  to  the  point  where  the 
ducts  of  the  sebaceous  glands  open    into   the   follicle.      Immediately  below 


THE    SKIN    AND    ITS    APPENDAGES. 


229 


(toward  the  papilla)  the  inner  root-sheath  begins  abruptly,  which  in  the  lower 
lx)rtion  of  the  follicle  is  differentiated  into  two  sharply-defined  layers;    the 


t 


Fig.  213. — Elements  op  Human  Haik  anu  Hair-Fullicl£.  X  240.  i.  Whitehair;  2.  scalesof  the  cuticle : 
3,  cells  of  the  cortical  substance  of  the  shaft ;  4.  cells  of  Huxley'-^  layer;  5,  cells  of  Henle's  layer,  having  the 
appearance  of  a  fenestrated  membrane  :  6,  cells  of  the  cortical  substance  of  the  root.     Techn.  No.  159. 


Connective- 
tissue  hair- 
follicle. 


Longitudinal  fibrous  layer. 

Circular  fibrous  layer. 
I  Glassy  membrane. 

Outer  root-sheath. 
f  Henle's  layer. 

[  Huxley's  layer. 

f  Sheath  and  hair-cuticle. 

I 

I    Cortical  substance. 

I    Mcdullarj'  Substance. 


Vi^.-- 


^'^^r^-;-- 


14.— From  a  Hn 


outer,   Hcnie  s   /oyer,  consists  of  a  single  or  double  row  of  epithelial  cells 
without  nuclei,  while  the  inner.  Hiix/t-y's  layer,  is  formed  of  a  simple  stratum 


230  HISTOLOGY. 

of  nucleated  cells.  The  inner  surface  of  this  layer  is  lined  by  a  delicate  mem- 
brane, the  cuticle  of  the  root-shealh,  which  exhibits  the  same  structure  as  the 
cuticle  of  the  hair.  Toward  the  base  of  the  follicle  the  outer  root-sheath 
diminishes  in  thickness  and  disappears ;  the  strata  of  the  inner  root-sheath 
lose  their  sharp  demarcation  and  are  gradually  transformed  into  the  spherical 
cells  of  the  hair-bulb. 

Devfxopment  of  the  H,\ir. 
The  first  anlage  of  the  hair  and  the  hair-follicle  appears  at  the  end  of  the 
third  embryonal  month  in  the  form  ot  a  local  thickening  of  the  epidermis, 
which  is  effected  chiefly  by  a  proliferation  of  the  cells  of  the  deepest  layer  of 
the  rete  mucosum.  This  thickening  grows  in  length  within  the  corium  and 
forms  a  solid  epidermal  peg — the  hair-germ— -yi^icYi  terminates  in  an  expanded, 


Fig.  =15.— From  a  Vertical  Section  (A)  OF  the  Skin  of  the  Cheek  of  a  Four  Months'  Human  Embryo 

AND     (B.     C,     D)     OF     THE     SkIN    OF     THE     FoREHEAD    OF     A     FiVE      MoNTHS'      HuMAN     EmBKVO.         X     80. 

E.  Epidermis,  consisting  throughout  of  niiclealed  epithelial  cells;  C,  corium  ;  x,  thickening  ;  /lyfe,  hair-germ  ; 
hi,  connective-tissue  hair-follicle  ;  /,  papilla  ;  aWj  outer  root-shealh  ;  s,  axial  portion,  in  which  in  the  upper 
division  the  separation  into  (/w)  an  inner  root-sheath,  and  (A)  the  hair  is  visible ;  /,  anlage  of  the  sebaceous 
glands.    Techn.  No.  i6i. 

club-shaped  extremity.  Meanwhile  the  papilla  and  the  dermal  portion  of  the 
hair-follicle  develop  by  differentiation  of  the  connective  tissue  of  the  surround- 
ing corium.  The  hair-germ  separates  into  an  outer  stratum  and  an  inner  axial 
cord.  The  former  becomes  the  outer  root-sheath ;  the  peripheral  portion  of 
the  axial  strand  becomes  the  inner  root-sheath  ;  the  central  part,  the  hair.  The 
sebaceous  glands  arise  as  local  outgrowths  of  the  outer  root-sheath  (Fig.  215). 
The  development  of  hairs  in  the  manner  described  may  occur  after  birth 
and  until  late  in  life. 


Growth  and  Shedding  of  the  Hair. 
The  growth  of  the   hair  is  effected  by  continual  mitotic  division  of  the 
epithelial  elements  around  the  papilla,  and  by  the  transformation  of  the  new 
cells  into  horny  elements  which  annex   themselves  from  below  to  previously 


THE    SKIN    AND    ITS    APPENDAGES.  23I 

cornified  cells.  Thus,  the  tip  is  the  oldest,  the  portion  lying  immediately 
above  the  hair-bulb  the  youngest  part  of  the  hair. 

At  birth  all  the  hairs  are  shed  and  replaced  by  others.  In  the  adult 
replacement  of  the  dead  hairs  of  the  scalp  and  beard  occurs  continually,  but 
not  periodically.  (With  regard  to  the  shedding  of  the  other  hairs  nothing  is 
definitely  known.) 

The  minute  details  of  the  process  are  as  follows  :  the  hair-bulb  becomes 
horny  and  frayed  like  a  brush  ;  the  now  dead  hair  is  .separated  from  the  papilla 
and  pushed  upward  by  the  pressure  from  below  of  the  young  elements  produced 
by  the  division  of  the  cells  around  the  papilla  ;  the  empty  root-sheaths  collapse  ; 
at  their  inferior  extremity  lies  the  hair-papilla  atrophied  and  altered  in  form 


Sebaceous  gland. 


—    Emply  root-sheath. 

.VUi'  ~~~^ Hair-papilla. 

Fig.  216. — From  a  Vektical  Shction  of  the  Hairy  Scalp  of  Adult  Man.     X  40-     Techn.  No.  162. 

(Fig.  216).  After  a  (often  long)  period  the  epithelial  elements  of  the  empty 
root-sheaths  begin  to  grow  and  form  a  new  hair-germ,  from  which  the  new 
hair  develops  by  the  same  processes  as  the  embryonal  hair.  The  new  hair 
pushes  upward  under  the  effete  hair,  which  after  a  shorter  or  longer  period 
falls  out. 

THE  GLANDS  OF  THE  SKIN. 
The  sebaceous  glands  are  either  unbranched  or  branched  simple  saccular 
glands.  Each  gland  consists  of  a  short  e.vcretory  duct  and  of  a  variable  num- 
ber of  acini.  The  duct  is  lined  by  stratified  scaly  epithelium,  an  extension  of 
the  outer  root -sheath,  which  undergoes  a  gradual  decrease  in  the  number  of  its 
layers  and  passes  into  the  epithelial  lining  of  the  acini.     This  consists  at  first 


232 


HISTOLOGY. 


of  low  cuboidal  cells,  that  are  followed  by  spherical  or  polyhedral  elements, 
varying  in  size,  which  fill  the  gland-sac  and  exhibit  all  the  transitional  phases 
in  the  process  by  which  the  cell  is  converted  into  the  secretory  product  of  the 
gland.  The  secretion,  the  sebum,  during  life  is  a  semifluid  substance  consisting 
of  fat  and  disintegrated  cells.  The  sebaceous  glands  occur  as  the  appendages 
of  the  hair-follicles  of  the  larger  hairs,  but  in  the  case  of  the  lanugo  hairs  these 
relations  are  apparently  reversed  and  the  follicles  of  the  latter  appear  as  the 
appendages  of  the  powerfully-developed  sebaceous  glands  (Fig.  217  A).  The 
sebaceous  glands  are  distributed  with  the  hair  over  the  entire  body,  and  are 
wanting  only  where  the  former  are  absent — on  the  palm  of  the  hand  and  on  the 
sole  of  the  foot.  There  are,  however,  sebaceous  glands  that  are  not  associated 
with  hair-follicles ;  for  e.xample,  on  the  red  edge  of  the  lips,  on  the  labia 
minora,  on  the  glans,  on  the  prepuce  of  the  penis ;  in  the  latter  situation  they 
are  known  as  Tyson's  glands.     The  sebaceous  glands  are  always  situated  in  the 


^ ^  Cell  with  wdl-devel- 

^  oped  drops  of  secre 


-«?s^  " /  Cu 


%.    -5  Cell  with  developing 
""  ~*       drops  of  secretion. 


G.  217.— .4.  Fr 
neum :  M,  re 
hair,  about  to  be  shed  ;  /z,  hair-folli 
From  a  Vertical  Section  of  th 
ceous  gtand  containing  gland-cells  i 


.D.  X  40.  C  Stratum  cor- 
duct  of  the  same;  ;f,  lanugo 
hair,  x,  is  forming. 

IF  THE  Ala  Nasi  of  an  Infant.     X  240.     Follicles  of  a  seba- 

stages  of  secretion.     Techn.  No.  162. 


Stratum  papillare  of  the  coriuni.  Their  size  varies  from  0.2  to  2.2  mm.;  the 
larger  are  found  in  the  integument  of  the  nose,  where  their  excretory  ducts  are 
visible  to  the  unaided  eye. 

The  coil-glands  (sudoriparous  or  sweat-glands)  are  long,  unbranched 
tubules,  whose  lower  ends  terminate  in  a  greatly  convoluted  spherical  mass, 
having  a  diameter  of  0.3  to  7  mm.  (of  the  latter  size  in  the  axilla).  Two  parts 
are  distinguished,  the  excretory  duct. a.nd  the  co//.  The  former  runs  a  straight 
or  a  sinuous  course  through  the  corium,  enters  the  epidermis  between  two 
papillae,  passes  in  a  spiral  through  the  stratum  corneum,  and  opens  on  the  sur- 
face of  the  skin  by  a  rounded  orifice,  the  sweat-pore,  just  visible  to  the  naked 
eye.  The  walls  of  the  duct  consist  of  longitudinally-disposed  bundles  of  fibrous 
connective  tissue,  lined  within  by  several  layers  of  cubical  epithelial  cells. 
The  coiV  is  a  greatly  convoluted  simple  canal,  the  walls  of  which  consist  of  a 


THE    SKIN    AND    ITS    APPENDAGES. 


'33 


simple  layer  of  cubical  cells,  containing  granules  of  pigment  and  of  fat,  sur- 
rounded by  a  delicate  membrana  propria.  In  well-developed  glands  longi- 
tudinally-disposed smooth  muscle-fibers  occur  between  the  membrana  propria 
and  the  gland-cells  (Fig.  208).  Branched  tubules  have  been  observed  only  in 
the  axillary  and  circumanal  glands. 

The  secretion  is  usually  an  oily  fluid  substance,  for  the  purjjose  of  lubricat- 
ing the  skin;  only  under  the  influence  of  altered  innervation  do  the  coil- 
glands  discharge  the  watery  liquid  called  sweat.  The  coil-glands  are  distrib- 
uted over  the  entire  surface  of  the  skin  and  are  absent  onlv  on  the  glans  and 


Fig.  si8.— From  a  V 

corneum  ;    sg,  retc  mucosum 
10  coil-glands  ;  *,  duct  of  the 


Skin  op  the  Sole  op  Human  Foot.  X  50.  sc.  Stratum 
,  vein ;  a'  7^,  branches  to  panniculus  adiposus  ;  a"  i''\  branches 
accompanying  this.     T'cchn.  No.  164. 


on  the  inner  surface  of  the  prepuce.      They  are  most  numerous  in  the  skin  of 
the  palm  of  the  hand  and  of  the  jilantar  surface  of  the  foot. 


THK    BLOOD-VESSELS,    LYiMPH -VESSELS,   AND   NERVES   OF    IHi: 

SKIN. 

The  artei-ies  originate  in  a  network  lying  over  the  fascia;  and  pass  upward 

to  the  surface  of  the  skin  ;    in  their  course  they  form  three  separate  capillary 

networks  lying  in  different  planes.     The  deepest  supplies  the  adipose  tissue  of 

the  subcutaneous  stratum  ;    that  occupying  the  next  level  ai)pears  in  the  form 


236  HISTOLOGY. 

within  and  between  the  gland-lobules.  Lymphatic  networks  also  occur  in  the 
vicinity  of  the  ampullae  and  the  areolae. 

The  nerves,  as  in  other  glands,  do  not  form  a  direct  connection  with  the 
secreting  cells,  but  probably  are  all  distributed  to  the  blood-vessels. 

Milk  microscopically  consists  of  a  clear  fluid,  the  milk  plasma,  in 
which  oil-globules,  2  to  5  /x  in  size,  are  suspended.  Owing  to  the  fact  that  the 
globules  do  not  coalesce,  the  presence  of  a  delicate  membrane  of  casein  is 
assumed.  In  addition,  isolated  cells  enclosing  oil-globules  (leucocytes?)  are 
found  in  the  milk. 

The  elements  of  the  milk  secreted  before  and  in  the  first  few  days  after 
parturition  include,  beside  the  oil-globules,  the  so-called  colostrum -corpuscles, 
nucleated  cells,  some  of  which  contain  minute  yellow-colored  and  larger  un- 
colored  fat-droplets,  others  only  uncolored  fat-droplets. 

The  mode  in  which  the  glandular  epithelium  participates  in  the  formation 
of  the  milk-globules  and  the  colostrum-corpuscles  is  not  yet  altogether  clear. 
Only  this  much  is  known  with  certainty,  that  the  cells  do  not  perish  in  the  act 
of  secretion.  It  is  a  question  whether  the  fat  within  the  glandular  cells  is 
discharged  alone  or  with  the  portion  of  the  cell  directed  toward  the  lumen  of 
the  acinus. 


X.    THE  EYE  AND   ITS  APPENDAGES. 

The  organ  of  vision  consists  of  the  eyeball,  the  optic  nerve,  the  eyelids, 
and  the  lacrymal  glands. 

THE  EYEBALL. 
The  eyeball  (bulbus  oculi)  is  a  hollow  globe,  which  encloses  formed  and 
fluid  contents.  The  walls  of  the  eyeball  are  composed  of  three  coats:  (i)  the 
tunica  externa,  a  fibrous  membrane  in  which  an  anterior  transparent  division, 
the  cornea,  may  be  distinguished  from  the  remaining  opaque  portion,  the  sclera  ; 
(2)  the  tunica  media,  rich  in  blood-vessels,  which  includes  three  divisions, — the 
choroid,  the  ciliary  body,  and  the  iris  ;  (3)  the  tunica  interna,  the  retina,  which 
contains  the  specialized  terminal  apparatus  of  the  optic  nerve.  The  formed 
contents  within  the  eyeball  are  the  lens  and  the  vitreous  body. 

The  Tunic.\  Extern.\. 
The  cornea  consists  of  five  strata,  which  enumerated  from  before  back- 
ward are  the  following  : — 

1.  The  anterior  epithelium. 

2.  The  anterior  basal  membrane. 
3    The  substance  proper. 

4.  The  posterior  basal  membrane. 

5.  The  posterior  endothelium. 


IHK    EYE    AND    ITS    APPENDAGES.  237 

The  anterior  epithelium  is  a  stratified  scaly  epithelium  consisting  of  a  lower- 
most layer  of  sharply-contoured  columnar  cells,  which  is  followed  by  three  or 
four  (more  in  animals)  layers  of  polyhedral  cells,  that  in  turn  are  covered  by 
several  strata  of  flattened  elements  still  possessing  nuclei.  The  thickness  of 
the  epithelium  in  man  is  0.03  mm.  At  the  rim  of  the  cornea  the  epithelium  is 
continuous  with  that  of  the  sclera. 

'Y\^t  anterior  basal  membrane  (Bowman's  membrane,  lamina  elastica  an- 
terior) in  man  is  a  conspicuous  stratum,  about  o.oi  mm.  thick,  and  almost 
homogeneous  in  appearance.  The  surface  is  provided  with  minute  serrations 
and  ridges  for  attachment  to  the  columnar  cells  of  the  anterior  epithelium. 
Posteriorly  it  pa.sses  gradually  into  the  substantia  propria  of  the  cornea,  of 
which  it  is  a  special  modification. 


Endothelium. 
Fig.  222. — Vertical  Shction  op  Human  Cornea.    X  loo.    Techn.  No.  169  b. 

The  j7//'jA?//(V/r(5/<v  constitutes  the  chief  bulk  of  the  cornea.  It  consists 
of  delicate  parallel  fibrilloe,  which  are  united  by  an  interfibrillar  cement-sub- 
stance into  bundles  of  nearly  uniform  thickness  ;  the  bundles  in  turn  are  united 
by  an  interfascicular  cement-substance  into  flat  lamellae,  which  lie  in  many 
superposed  strata  and  are  held  together  by  an  interlamellar  cement-substance. 
The  lamellae  are  arranged  parallel  to  the  surface  of  the  cornea  and  run  in  merid- 
ional curves  one  above  the  other,  so  that  a  vertical  section  through  the  center 
of  the  cornea  shows  alternate  longitudinal  and  transverse  bundles.  A  number 
of  bundles  running  obliquely,  the  so-called  arcuate  fibers,  unite  each  lamella 
with  its  neighbor  above  or  below  ;  especially  well-developed  arcuate  fibers 
occur  in  the  anterior  strata  of  the  substantia  propria. 

Embedded  in  the  cement-substance  is  an  intercommunicating  system  of 
branched  canaTiculi,  the  lymph-ianalietili,  which  at  many  places  are  expanded 
to  broad  oval  lacunce,  the  corneal  spaces.  The  latter  lie  between  the  lamellae, 
while  the  canaliculi  also  penetrate  between  the  bundles.  The  lacunre  and 
canaliculi  contain  a  serous   fluid   and   cells. — "  fixed  "   corneal  corpuscles  and 


236  HISTOLOGY. 

within  and  between  the  gland-lobules.  Lymphatic  networks  also  occur  in  the 
vicinity  of  the  ampullae  and  the  areolae. 

The  nerves,  as  in  other  glands,  do  not  form  a  direct  connection  with  the 
secreting  cells,  but  probably  are  all  distributed  to  the  blood-vessels. 

Milk  microscopically  consists  of  a  clear  fluid,  the  milk  plasma,  in 
which  oil-globules,  2  to  5  /.t  in  size,  are  suspended.  Owing  to  the  fact  that  the 
globules  do  not  coalesce,  the  presence  of  a  delicate  membrane  of  casein  is 
assumed.  In  addition,  isolated  cells  enclosing  oil-globules  (leucocytes?)  are 
found  in  the  milk. 

The  elements  of  the  milk  secreted  before  and  in  the  first  i^^v  days  after 
parturition  include,  beside  the  oil-globules,  the  so-called  colostrum-corpuscles, 
nucleated  cells,  some  of  which  contain  minute  yellow-colored  and  larger  un- 
colored  fat-droplets,  others  only  uncolored  fat-droplets. 

The  mode  in  which  the  glandular  epithelium  participates  in  the  formation 
of  the  milk-globules  and  the  colostrum-corpuscles  is  not  yet  altogether  clear. 
Only  this  much  is  known  with  certainty,  that  the  cells  do  not  perish  in  the  act 
of  secretion.  It  is  a  question  whether  the  fat  within  the  glandular  cells  is 
discharged  alone  or  with  the  portion  of  the  cell  directed  toward  the  lumen  of 
the  acinus. 


X.    THE  EYE  AND   ITS  APPENDAGES. 

The  organ  of  vision  consists  of  the  eyeball,  the  optic  nerve,  the  eyelids, 
and  the  lacrymal  glands. 

THE  EYEBALL. 
The  eyeball  (bulbus  oculi)  is  a  hollow  globe,  which  encloses  formed  and 
fluid  contents.  The  walls  of  the  eyeball  are  composed  of  three  coats:  (i)  the 
tunica  externa,  a  fibrous  membrane  in  which  an  anterior  transparent  division, 
the  cornea,  may  be  distinguished  from  the  remaining  opaque  portion,  the  sclera  ; 
(2)  the  tunica  media,  rich  in  blood-vessels,  which  includes  three  divisions, — the 
choroid,  the  ciliary  body,  and  the  iris  ;  (3)  the  tunica  interna,  the  retina,  which 
contains  the  specialized  terminal  apparatus  of  the  optic  nerve.  The  formed 
contents  within  the  eyeball  are  the  lens  and  the  vitreous  body. 

The  Tunica  Extern.\. 
The  cornea  consists  of  five  strata,  which  enumerated  from  before  back- 
ward are  the  following  : — 

1.  The  anterior  epithelium. 

2.  The  anterior  basal  membrane. 
3    The  substance  proper. 

4.  The  posterior  basal  membrane. 

5.  The  posterior  endothelium. 


THE    EVE    AND    ITS    APPENDAGES.  237 

The  anterior  epithelium  is  a  stratified  scaly  epithelium  consisting  of  a  lower- 
most layer  of  sharply-contoured  columnar  cells,  which  is  followed  by  three  or 
four  (more  in  animals)  layers  of  polyhedral  cells,  that  in  turn  are  covered  by 
several  strata  of  flattened  elements  still  possessing  nuclei.  The  thickness  of 
the  epithelium  in  man  is  0.03  mm.  At  the  rim  of  the  cornea  the  epithelium  is 
continuous  with  that  of  the  sclera. 

The  anterior  basal  membrane  (Bowman's  membrane,  lamina  elastica  an- 
terior) in  man  is  a  conspicuous  stratum,  about  o.oi  mm.  thick,  and  almost 
homogeneous  in  appearance.  The  surface  is  provided  with  minute  serrations 
and  ridges  for  attachment  to  the  columnar  cells  of  the  anterior  epithelium. 
Posteriorly  it  pa.sses  gradually  into  the  substantia  propria  of  the  cornea,  of 
which  it  is  a  special  modification. 


Endothelium. 
Fig.  222. — Vertical  Section  of  Human  Cornea.     X  loo.    Techn.  No.  169  b. 

The  substance  proper  constitutes  the  chief  bulk  of  the  cornea.  It  consists 
of  delicate  parallel  fibrillie,  which  are  united  by  an  interfibrillar  cement-sub- 
stance into  bundles  of  nearly  uniform  thickness  ;  the  bundles  in  turn  are  united 
by  an  interfascicular  cement-substance  into  flat  lamellae,  which  lie  in  many 
superposed  strata  and  are  held  together  by  an  interlamellar  cement-substance. 
The  lamellre  are  arranged  parallel  to  the  surface  of  the  cornea  and  run  in  merid- 
ional curves  one  above  the  other,  so  that  a  vertical  section  through  the  center 
of  the  cornea  shows  alternate  longitudinal  and  transverse  bundles.  A  number 
of  bundles  running  obliquely,  the  so-called  arcuate  fibers,  unite  each  lamella 
with  its  neighbor  above  or  below  ;  especially  well -developed  arcuate  fibers 
occur  in  the  anterior  strata  of  the  substantia  propria. 

Embedded  in  the  cement-substance  is  an  intercommunicating  system  of 
branched  cana*liculi,  the  lymph-canaliculi,  which  at  many  places  are  expanded 
to  broad  oval  lacuna:,  the  corneal  spaces.  The  latter  lie  between  the  lamellae, 
while  the  canaliculi  al.so  penetrate  between  the  bundles.  The  lacunre  and 
canali<uli  contain  a  serous   fluid   and   cells, — "  fixed  "   corneal  corpuscles  and 


238 


HISTOLOGY. 


7vanileriiig  cells.       The  corneal  corpuscles   are  flattened  connective-tissue  cells 
possessingHarge  nuclei  ;  they  lie  against  one  wall  of  the  lacunae  (Fig.  224). 

The  posterior  basal  membrane  (membrane  of  Descemet,  lamina  elastica 
posterior)  is  a  clear,  glassy  elastic  layer,  0.006  mm.  thick.  In  adult  man 
the  posterior  surface,  at  the  periphery  of  the  cornea,  is  beset  with  hemispherical 
protuberances. 


Lymph-canalicul 


:al  spaces 


Fig.  223.— Horizontal  Section  of  Cornea  of  Ox. 
Silver-preparation;  negative  picture  ;  the  canalicular 
system  is  light  upon  a  dark  ground.  X  about  240. 
Techn.  No.  173. 


Corneal  corpuscles. 

Fig.  224. — Horizontal  Section  of  Cornea  op 
Rabbit.  Positive  picture.  X  about  240.  lechn. 
No.  174. 


The. posterior  endothelium  is  composed  of  a  single  la)-er  of  flat  j)olygonal 
cells  with  slightly  projecting  nuclei. 

The  sclera  consists  principally  of  interlacing  bundles  of  fibrous  connective 
tissue,  extending  for  the  most  part  in  meridional  and  equatorial  directions.     In 


[HE    EVE    AND    ITS    APPENDAGES. 


239 


addition,  delicate  elastic  fibers  arranged  in  networks  and  flattened  connective- 
tissue  cells  are  present;  the  latter,  like  the  corneal  corpuscles,  lie  in  lacunae, 
which  differ  from  the  corneal  spaces  only  in  having  more  irregular  outlines. 
Between  the  sclera  and  the  choroid  is  a  layer  of  loose,  highly-elastic  tissue  con- 
taining branched  pigmented  cells  and  flattened  elements  free  from  pigment 
("endothelial"  cells).  On  separating  the  two  coats  a  portion  of  this  tissue 
adheres  to  each  ;  that  on  the  sclera  is  called  the  lamina  fiisca  sclera,  that  on 
the  choroid,  lamina  siiprachoroidea. 

The  sclera  is  thickest  posteriorly  (i  mm.),  and  becomes  gradually  thinner 
toward  the  cornea. 

The  Tunica  Media. 
The  choroid  is  characterized  by  the  great  abundance  of  its  blood-vessels, 
which  are  arranged  in  two  layers.      The  superficial  layer,  adjoining  the  lamina 
suprachoroidea,  the  layer  of  large  blood-vessels,  comprises  the  ramifications  of 


Fig.  226.— yl.  From  , 

fibers ;  k,  nucleus  of  a  flat  nonpigmenled  cell ;  the  cell  I 
B.  Portion   op    Human  Choriocapillakis  and  the  A 

capillaries,  some  of  which  contain  (^)   blood-corpuscle 

work."    Techn.  No.  170  a. 


X  240.     /.  Pigment  cells;    ^,  elastic 


the  arterial  and  venous  channels,  which  are  embedded  in  a  supporting  tissue  called 
the  stroma,  consisting  of  networks  of  fine  elastic  fibers  and  numerous  branched 
pigment-cells.  In  addition,  the  stroma  contains  the  tissues  accompanying  the 
large  arteries  ;  namely,  fibrillar  connective  tissue,  smooth  muscle-fibers,  and 
nonpigmcnted  plate-like  cells  united  in  delicate  endothelial  membranes. 
The  deeper  layer,  the  mcmbrana  choriocapillaris,  or  layer  of  capillary  networks, 
is  composed  of  a  narrow-meshed  net  of  capillaries,  between  which  no  formed 
elements  are  found.  Between  the  two  layers  of  blood-vessels  lies  the 
boundary  zone,  a  portion  of  the  stroma  consisting  of  networks  of  fine  elastic 
fibers  and  almost  devoid  of  pigment.  In  ruminants  and  horses  this  zone  con- 
sists of  wavy  bundles  of  connective  tissue,  to  which  is  due  the  metallic  reflex 
seen  in  the  eyes  of  these  animals.  This  shining  membrane  is  known  as  the 
tapetiim  fibrosum.  The  similar  iridescent  tapetum  cellulosiim  of  carnivora  is 
composed  of  several  strata  of  plate-like  cells  containing  numerous  minute 
crystals. 


HISTOLOGY. 


Attached  to  the  membrana  choriocapillaris  is  the  ^^/assy  mcmluane  or 
vitreous  lamina,  a  structureless  lamella,  about  2  n  thick,  possessing  delicate 
lattice-like  markings  on  its  outer  surface.     The  polygonal  areas  observed  on  its 


2.  Connective-tissue  of  the  conjunct 
al,  6,  circular  fibers  of  ciliary  muscl 
retina.  lo.  Stroma  of  tiie  iris,  ii, 
I ;   13,  epithelium.     14.  Venous  sinus 


NGLH  OF  Man.  X  30.  I.  Epithe- 
:lera.  4,  5,  6,  7,  and  8.  Ciliary  body;  4,  meridional, 
y  process;  8,  ciliary  portion  of  retina.  9  Iridal  por- 
.  Cornea;  11 ,  posterior  elastic  lamina;  12,  substantia 
15.  .\ngle  of  iris.    Techn.  No.  169  a. 


inner  surface  are  patches  of  retinal  pigment.  The  glassy  membrane  approaches 
in  character  the  elastic  membranes. 

The  ciliary  body  is  formed  by  the  ciliary  processes  and  the  ciliary  muscle. 

The  ciliary  processes  are  seventy  or  eighty  meridionally-placed  folds, 
which  begin  low  at  the  ora  serrata,  gradually  attain  a  height  of  i  mm.,  and 
terminate  with  an  abrupt  descent   near  the  edge  of  the  lens.      Each   ciliary 


S-iTyf, 


Endothelial  nucle 


3.  Vascular  layc 


Posterior  boundary 
layer. 


Fig  228.— Vertical  Section  op  Puhillakv  1'..„ti..w  ..f  Human  Ikis,  ,  ico.  About  one-fifth  of  the 
width  of  the  ins  is  shown,  g.  Blood-vessel,  vifith  thiclc  connective-tissue  sheath  ;  lit,  sphincter  pupillse 
cle,  cut  transversely  ;  p^  pupillary  border  of  the  iris.     Techn.  No.  170  c. 


process  consists  of  fibrillar  connective  tissue  containing  numerous  blood-vessels 
and  inwards  is  limited  by  a  continuation  of  the  glassy  membrane,  which  here 
is  distinguished  by  minute  intersecting  folds. 


THE    EYE    AND    ITS    APPENDAGES.  24I 

The  ciliaij  muscle  is  an  annular  band,  about  3  mm.  broad,  anteriorly  0.8 
mm.  thick,  arising  from  the  inner  wall  of  Schlemm's  canal.  The  nonstriped 
elements  of  which  it  is  composed  extend  in  three  different  directions  :  (i) 
meridional  fibers,  numerous  fasciculi  running  parallel  to  the  sclera,  which  reach 
to  the  smooth  portion  of  the  choroid  and  are  known  as  the  tensor  choroidea:  ; 
(2)  radial  fibers,  lying  next  to  the  meridional  bundles,  which  from  without  in- 
ward progressively  assume  a  more  radial  disposition  (oriented  to  the  center  of 
the  bulbus  oculi)  and  posteriorly,  still  in  the  region  of  the  ciliary  body,  turn 
and  follow  a  circular  course  ;  (3)  (ircular  (equatorial)  fibers,  the  so-called 
ring-muscle  of  Alii  Her. 

The  iris  consists  of  a  stroma  arranged  in  three  layers,  covered  anteriorly 
by  a  continuation  of  the  posterior  endothelium  of  the  cornea  and  posteriorly  by 
a  modified  extension  of  the  retina.  Accordingly  five  layers  may  be  dis- 
tinguished : — 

1.  The  anterior  endothelium. 

2.  The  anterior  boundary  layer. 

3.  The  vascular  layer. 

4.  The  posterior  boundary  layer. 

5.  The  pigment  layer. 

The  anterior  endothelium  covers  the  anterior  surface  of  the  iris  and,  like 
that  on  the  posterior  surface  of  the  cornea,  consists  of  a  single  layer  of 
flattened  polygonal  cells. 

Tiie  anterior  boundary  layer  (reticular  layer)  comprises  three  or  four  strata 
of  networks,  which  are  formed  by  stellate  connective-tissue  cells  ;  it  resembles 
the  reticulum  of  adenoid  tissue.  The  posterior  stratum  pa.sses  gradually  into 
the  adjoining  vascular  stroma. 

The  vascular  layer  of  the  iris  contains  numerous  radially-disposed  (to  the 
pupilj  blood-vessels  embedded  in  a  stroma  consisting  of  slender,  loosely- 
united  bundles  of  connective  tissue.  The  blood-vessels  and  nerves  are  pro- 
vided with  conspicuously  thick  connective-tissue  sheaths.  The  smooth  muscle- 
fibers  in  the  vascular  stroma  are  arranged  in  two  sets,  as  annular  bundles 
encircling  the  pupillary  margin  of  the  iris,  a  zone  about  i  mm.  in  width 
constituting  the  sphincter  of  the  pupil,  and  as  a  it.\\  radially-disposed  bundles, 
which  do  not  form  a  continuous  layer — the  dilator  of  the  pupil.  In  the 
anterior  boundary  layer  and  in  the  vascular  stroma  pigmented  cells  occur  in 
greatly  varying  numbers  ;  in  blue  eyes  they  are  absent. 

The  posterior  boundary  layer  is  a  clear,  glassy,  homogeneous  membrane, 
elastic  in  its  nature. 

The  pigment  layer  of  the  iris  (pars  iridica  retinje)  comprises  two  layers,  of 
which  the  anterior  contains  spindle-shaped,  the  posterior  polygonal  pigment- 
cells.  Both  layers  are  so  crowded  with  pigment-granules  that  recognition  of 
the  individual  elements  is  usually  impossible.  The  pigment  is  wanting  only  in 
albinos.  The  posterior  surface  of  the  pigment  layer  is  covered  by  an  exceed- 
ingly delicate  membrane,  the  membrana  limitans  iridis,  a  continuation  of  the 
nicmbrana  limitans  interna  retinae. 


242  HISTOLOGY. 

The  Iricio- Corneal  Angle. — The  juncture  of  the  sclera  and  the  cornea 
is  of  especial  interest,  since  here  the  iris,  the  cornea,  and  the  ciliary  body  meet. 
The  transformation  of  the  sclera  into  the  cornea  is  absolutely  direct ;  the  wavy 
bundles  of  the  sclera,  without  interruption  in  continuity,  pass  over  into  the 
straight  bundles  of  the  cornea,  the  system  of  canaliculi  of  the  sclera  communi- 
cates with  that  of  the  cornea.  The  line  of  transition  is  oblique,  and  micro- 
scoi)ically  not  sharply  defined,  because  the  transformation  of  the  sclera  into  the 
tissues  of  the  cornea  takes  place  soonest  in  the  posterior  strata  of  the  tunica 
externa.  At  the  periphery  of  the  cornea  the  posterior  basal  membrane  and  the 
hindermost  laminse  of  the  substance  proper  meet  the  ciliary  border  of  the  iris  and 
form  the  irido-cortieal  angle.  Here  the  iris  sends  toward  the  posterior  surface 
of  the  posterior  basal  membrane  connective-tissue  processes,  that,  well  developed 
in  animals,  constitute  the  so-called  ligamentum  iridis  pectinatiim.  In  man  these 
processes  are  inconspicuous.  At  the  periphery  of  the  cornea  the  posterior  basal 
membrane  splits  up  into  fibers  which,  strengthened  by  elastic  fibers  from  the 
intramuscular  connective  tissue  of  the  ciliarv  muscle  and  from  the  elastic  ten- 


11  layer, 
fiber  layer. 

Fig.  Z2Q. — Vertical  Section  of  Human  Retina.  X  240.  The  nerve-fiber  layer  has  been  cut  transversely 
ana  is  very  thin,  because  the  section  was  not  taken  from  the  posterior  segment  of  the  eye.  b.  Blood-vessel ; 
k^  expanded  base  of  radial  fiber.     I'echn.  No.  170  d. 

dons,  also  with  accessions  in  a  lesser  degree  from  the  sclera,  blend  with  the 
iridal  processes.  The  tissues  participating  in  the  formation  of  the  loose  mass  of 
fibers  occupying  the  angle  of  the  iris  are  derived  from  the  structures  that  meet 
one  another  at  the  irido-corneal  angle  :  cornea,  sclera,  iris,  and  ciliary  muscle. 
The  posterior  endothelium  of  the  cornea  continued  on  to  the  surface  of  the  iris 
forms  a  sheath  for  these  fibers.  The  spaces  between  them,  in  direct  connection 
with  the  anterior  chamber  of  the  eye  and  containing  the  same  fluid,  are  called 
the  spaces  of  Foutana.     In  man  they  are  but  slightly  developed. 


The  Tunica  Interna. 

The  retina  extends  from  the  entrance  of  the  optic  nerve  to  the  pupillary 

margin  of  the  iris,  and  in  this  tract  three  zones  may  be  distinguished  :    (i)  the 

pars  optica  retince,  the  entire  expansion  of  the  optic  nerve  ;   (2)  the  pars  ciliaris 

retince,  extending  from  the  ora  serrata  to  the  ciliary  margin  of  the  iris  ;   (3)  the 


Cerebral  lamina. 


THE    EYE    AXD    ITS    APPENDAGES.  243 

pars  iridiia  rctiiur,  which  covers  the  posterior  surface  of  the  iris  from  the  cili- 
ary to  the  pupillary  margin. 

The  pars  optica  retiriie,  the  portion  of  the  retina  alone  sensitive  to  light, 
lines  the  entire  posterior  .segment  of  the  eyeball  and  extends  to  within  a  short 
distance  of  the  ciliary  body,  where  it  terminates  in  a  sharp,  macroscopically 
perceptible,  serrated  line,  the  o)a  scrrata.  It  falls  into  two  divisions,  an  outer 
neiiro-epithelial  lamina,  and  inner  cerebral  lamina.  In  each  of  these  divisions 
several  layers  may  be  distinguished — four  in  the  neuro-epithelial  lamina,  five 
in  the  cerebral  lamina;  if  the  pigment  layer  lying  close  beneath  the  choroid, 
which  genetically  belongs  to  the  retina,  is  added,  there  are  ten  layers,  which 
from  without  inward  are  arranged  in  the  following  order  :  — 

1.  The  pigment  layer. 

2.  The  layer  of  rods  and  cones.  -\ 

3.  The  membrana  limitans  e.xterna.       -  Neuro-epithelial  lamina. 

4.  The  outer  granule  layer.  J 

5.  The  fiber-layer  of  Henle. 

6.  The  outer  reticular  layer. 

7.  The  inner  granule  layer. 

8.  The  inner  reticular  layer. 

9.  The  ganglion-cell  layer. 
10.  The  nerve-fiber  layer.*        j 

The  elements  of  the  preceding  layers  are  only  in  part  nervous,  or  epithelial, 
in  their  nature  ;  the  other  part  is  formed  of  the  supporting  substance,  which  how- 
ever is  not  of  the  nature  of  connective  tissue.  The  most  conspicuous  elements 
of  the  supporting  tissue  are  the  radial  fibers  of  Afiiller,  elongated  cells  which 
extend  from  the  inner  surface  of  the  retina  through  all  the  layers  to  the  rods 
and  cones.  The  inner  end  of  the  fibers  is  characterized  by  a  conical  foot, 
and  they  are  so  closely  placed  that  the  expanded  bases  apparently  produce  a 
continuous  membrane  on  the  inner  surface  of  the  retina,  the  so-called  mem- 
brana limitans  interna.  From  the  apex  of  the  pyramidal  base  the  fibers  pro- 
ceed, with  progressive  decrease  in  thickness,  through  the  inner  reticular  layer 
to  the  inner  granule  layer,  where  they  are  provided  with  a  nucleus  ;  from  here 
they  pass  through  the  outer  reticular  and  outer  granule  layer  to  the  external 
limiting  membrane,  with  which  they  unite.  Throughout  their  entire  course 
the  radial  fibers  give  off  lateral  processes  for  the  support  of  the  nervous  ele- 
ments. In  addition  to  these  elongated  radial  cells,  concentric  supporting  cells 
are  found  in  the  outer  reticular  layer  ;  they  extend  parallel  to  the  surface,  are 
jirovided  with  long  processes,  are  in  part  nucleated,  in  part  nonnucleated. 
From  the  surface  of  the  membrana  limitans  externa  delicate  processes  extend  to 
the  rods  and  cones,  the  bases  of  which  they  embrace  as  the  so-called  fiber- 
crates.     A  portion  of  both  the  reticular  layers  belongs  to  the  supporting  sub- 


*  To  these  the  membrana  limitans  interna  is  sometimes  added  as  an  elevenlli  layer  ;  it,  how- 
ever, <loes  not  represent  an  independent  membrane. 


244  HISTOLOGY. 

Stance,  and  also  the  small   quantity  of  cement-substance  in  the  ganglion -cell 
layer. 

In  the  more  detailed  description  of  the  individual  layers  of  the  retina  the 
series  will  be  taken  up  in  the  reverse  order,  from  within  outward. 

The  Cerebral  Layer. 

The  nerve-fiber  layer  consists  of  naked  axis-cylinders  arranged  in  bundles 
and  united  in  a  sort  of  plexus.  From  the  entrance  of  the  optic  nerve,  where 
the  fiber-layer  is  thickest,  the  fibers  extend  outward  in  a  radial  direction  to 
the  ora  serrata.  The  radial  arrangement  of  the  fibers  is  disturbed  in  the  region 
of  the  macula  lutea.  The  majority  of  the  axis-cylinders  are  centripetal  fibers 
which  originate  in  the  ganglion-cell  layer  of  the  retina  ;  the  smaller  portion 
are  the  axis-cylinder  processes  of  cerebral  ganglion-cells,  centrifiigal  fibers, 
which  ramify  in  the  inner  nuclear  layer  and  terminate  in  free  endings. 

The  ganglion-cell  layer  consists  of  a  single  row  of  large  multipolar  ganglion- 
cells,  whose  imbranched  axis-cylinder  processes  are  centrally  directed,  toward 
the  nerve-fiber  layer,  whose  one  or  more  branched  protoplasmic  processes  ex- 

Pigment  epithelii 

Rods  and  cones.  |    '11,^, 
Externa!  limiting  membrane. 


uie  lay 


,^ 


eticular  lay 


Ganglion-cell  layei 


---    / 


Fig.  230. — Vertical  Section  of  Retina  of  Rabbit.     X  240.     k.  Expanded  base  of  radial  fibers;  «,  nucle- 
ated portion  of  the  same  :  I,  "  membrana  limitans  interna."      Techn.  No.  170  d, 

tend  peripherally,  toward  the  inner  reticular  layer  ;  there  they  divide  and  are 
arranged  in  delicate  feltworks  parallel  to  the  surface,  and  with  the  processes 
from  other  ganglion-cells  form  a  dense  nervous  tangle. 

The  inner  reticular  layer  consists  of  an  exceedingly  delicate  network  of 
sustentacular  tissue,  which  supports  a  dense  fiber-maze  in  the  formation  of 
which  processes  of  all  the  ganglion -cells  of  the  retina  participate. 

The  inner  granule  layer  includes  elements  which  differ  greatly  in  their 
nature.  The  innermost  stratum  consists  of  large  ganglion-cells,*  which  send 
branched  processes  into  the  inner  reticular  layer.  From  many  of  these  cells — 
but  not  all — an  axis-cylinder  process  passes  to  the  nerve-fiber  layer.     The  re- 


*  These  cells  were  formerly  called  spongioblasts,  because  they  were  erroneously  regarded 
as  the  producers  of  the  "  neuro-spongium  "  (inner  reticular  layer) ;  they  are  elements  of  the 
ganglion  of  the  optic  nerve  which  have  not,  like  the  other  elements,  wandered  through  the 
inner  reticular  layer. 


THE    EYE    AND    ITS    APPENDAGES. 


245 


maining  strata,  for  the  greater  part,  are  composed  of  small  bipolar  ganglion-cells 
(ganglion  retina),  whose  central  process  extends  into  the  inner  reticular  layer, 
where  it  breaks  up  into  delicate  varicose  branches;  while  the  peripheral  process 
reaches  to  the  outer  reticular  layer,  where  it  divides  into  branches  extending 
parallel  to  the  surface  and  resolves  into  extremely  minute  fibrills,  which  pass 
into  a  subepithelial  tangle  formed  by  the  felting  of  processes  of  neighbor- 
ing ganglion-cells.  All  bipolar  ganglion-cells  send  up  a  process  between  the 
visual  cells,  where,  near  the  membrana  limitans,  it  terminates  in  a  minute  knob. 
The  nuclei  of  the  radial  fibers  occur  in  this  layer. 


Fig.  231.— Schemh  op  ■ 


HH  Elements  of  the  Rbti 
ments,  that  on  the  right  thi 


the  figure  on  the  left  represents  the  supporting  ele- 
id  epithelial  elements. 


At  the  border  of  this  zone,  next  to  the  outer  reticular  layer,  lie  small  and 
large  stellate  cells  ;  they  send  many  jjrocesses  to  participate  in  the  formation  of 
the  subepithelial  network  ;  one  process  extends  to  the  inner  reticular  layer, 
where  it  terminates  in  minute  branches,  and  another — the  axis-cylinder  process — 
after  a  long  horizontal  course,  bends  and  passes  in  a  vertical  direction  to  the 
nerve-fiber  layer.  According  to  other  authors  this  process  ends  in  the  outer 
reticular  layer,  where  its  ramifications  surround  the  base  of  the  visual  cells. 

The  outer  reticular  layer  (subepithelial  layer)  is  likewise  a  delicate  net- 
work of  sustentacular  tissue,  which  supports  the  nervous  tangle  just  described. 
The  cellular  elements  of  this  layer  include  the  concentric  sustentacular  cells 
and  the  subejiithelial  ganglion-cells ;  the  latter  are  displaced  elements  of  the 
ganglion  retina;,  which   differ  from   the   bipolar   ganglion-cells  only  in  their 


246  HISTOLOGY. 

rounded  form,  agreeing   entirely  with   the  latter  in   regard   to   their  terminal 
ramifications. 

The  Neuro-epithelial  L.-wer. 

The  neuro-epithelial  layer  consists  of  two  kinds  of  elements,  the  rod- 
visual  cells  and  the  cone-visual  cells,  which  are  both  characterized  by  the  situa- 
tion of  the  nucleus  in  the  lower  half  of  the  cell  and  the  sharp  demarcation  of 
the  upper  nonnucleated  division  from  the  lower  portion  by  the  perforated 
membrana  liraitans  externa.  This  gives  rise  to  the  appearance  of  different 
layers,  the  inner  nucleated  portion  of  the  visual-cells  being  known  as  the  outer 
granule  layer,  the  outer  nonnucleated  division  as  the  layer  of  rods  and  cones. 
Between  these  two  lies  the  limiting  membrane. 

The  Rod-Visual  Cells. — The  outer  halves  of  these  elements  are  the 
rods,  slender  cylinders  (60  //  long,  2  ti.  thick),  which  consist  of  a  homogene- 
ous outer  segment  and  a  finely-granular  inner  segment.      The  outer  segment  is 


2{ 


^     "%-< 


■1O 


0 


Fig.  232.— Isolated  Elements  of  Retina  of  Ape.  X  240.  ■■  Mutilated  ganglion-ccU  of  the  ganglion  of 
the  optic  nerve.  2.  Elements  of  the  inner  granule  layer.  3.  Rod-visual  cells  and  fragments  of  the  same  ; 
below,  two  outer  segments,  one  of  which  exhibits  transverse  striation,  the  beginning  of  a  disintegration  inio 
transverse  platelets  ;  above  are  two  rods,  the  outer  segment  of  the  lower  shows  beginning  disintegration  ; 
the  uppermost  figure  shows  more  complete  rod-cells ;  a,  outer  segment .  /,  inner  segment ;  k,  nucleus  of  rod  ; 
J-,  fiber-body.  4.  Cone-visual  cells  ;  </,  outer  seement ;  i,  inner  segment ;  k,  nucleus  of  cone  :  y,  cone-fiber, 
torn  at  lower  end;  .r,  fiber-body.  5.  Radial  fiber;  /.-,  nucleus  of  the  same;  r,  expanded  base  of  radial- 
fiber.     Techn.  No.  172. 

the  exclusive  seat  of  the  visual  purple.  The  inner  segment  possesses  in  its 
outer  end  an  ellipsoidal,  fibrillated  body,  the  fiber-body.  The  inner  halves  of 
the  rod-visual  cells  are  named  rod-fibers  ;  they  are  exceedingly  delicate  filaments 
which  are  provided  with  nucleated  expansions,  the  rod-granules.  The  nuclei 
are  marked  by  one  to  three  light  transverse  bands.  The  basal  end  of  the  cell 
is  prolonged  as  a  minute  process,  terminating  in  a  free,  club-shaped  expansion 
(Fig.  231). 

The  Cone-Visual  Cells. — The  outer  halves  of  these  cells,  the  cones,  con- 
sist likewise  of  an  outer  segment  and  inner  segment.  The  outer  segments  are 
conical  and  shorter  than  those  of  the  rods.  The  inner  segments  are  thick  and 
expanded,  and  the  cone  is  therefore  flask-shaped.  The  inner  segment  of  the 
cones  also  contains  a  fiber-body.  The  inner  halves  of  the  cone-visual  cells  are 
the  cone-fibers  ;  these  are  broad  and  rest  with  a  pyramidal  expansion  or  foot  on 
the  outer  reticular  layer.  The  nucleated  enlargement,  the  cone-granule,  usually 
lies  to  the  inner  side  of,  and  close  to,  the  membrana  limitans. 


THE    EVE    AND    ITS    APPENDAGES. 


247 


248  HISTOLOGY. 

The  number  of  the  rods  is  much  greater  than  that  of  the  cones.  The  lat- 
ter occur  at  regular  intervals,  so  that  three  to  four  rods  lie  between  two  cones 
(Fig.  229). 

The  basal  portions  of  the  visual  cells,  resting  upon  the  outer  reticular  layer, 
are  usually  plainly  to  be  recognized  as  a  peculiar  radially-striated  layer — Hcnle  s 
fiber-layer ;  in  the  region  of  the  macula  lutea  this  fiber-layer  is  particularly 
broad  ;  it  gradually  diminishes — often  very  unsymmetrically — toward  the  era 
serrata. 

The  pigmented  epitheliiDii  consists  of  a  simple  layer  of  hexagonal  cells, 
which  in  the  outer  zone,  toward  the  choroid,  where  the  nucleus  lies,  are  free 
from  pigment,  while  their  inner  division  contains  numerous  rod-shaped  pig- 
ment-granules, I  to  5  IX  long.  From  the  inner  division  numerous  delicate  pro- 
cesses extend  between  the  rods  and  cones.  In  albinos  and  on  the  tapetum  the 
epithelium  is  free  from  pigment. 

In  the  region  of  the  macula  lutea  and  fovea  centralis,  also  of  the  ora  ser- 
rata, the  structure  of  the  retina  above  described  presents  modifications  calling 
for  special  consideration. 

At  the  macula  the  layers  of  the  retina  exhibit  the  following  variations. 
Delicate  fibers  of  the  optic  nerve  run  direct  from  the  entrance  of  the  latter  to 
the  adjacent  median  portion  of  the  macula ;  above  and  below  these  fibers, 
thicker  nerve-fibers  run  from  the  optic  entrance  convexly  upwards  and  down- 
wards and  unite  at  the  lateral  margin  of  the  macula.  The  ganglion-cell  layer 
has  greatly  increased  in  thickness,  owing  to  the  development  of  the  layer  of 
bipolar  ganglion-cells,  which  instead  of  a  single  row  are  arranged  in  many  (up 
to  9)  rows  one  above  the  other  ;  also  the  inner  granule  layer  by  multiplication 
of  its  elements  has  become  almost  twice  as  broad.  The  inner  and  outer  granule 
layers  suffer  no  essential  change.  The  neuro-epithelial  layer  is  here  represented 
by  the  somewhat  smaller  cone-visual  cells  alone.  The  rod-visual  cells  diminish 
in  number  at  the  margin  of  the  macula,  and  within  the  macula  they  are  wanting 
altogether  ;  as  a  result  the  cone-fibers  are  visible  in  a  wide  extent :  they  form 
here  the  fiber-layer  of  Henle.  The  cone-granules,  on  account  of  their  large 
number,  lie  in  several  rows  one  above  the  other. 

Toward  'C<\t  fovea  centralis  in  the  center  of  the  macula  the  layers  of  the 
retina  become  gradually  thinner  and  in  part  totally  suspended.  At  first, 
with  the  exception  of  a  few  fibers,  the  nerve-fiber  layer  disappears,  then  the 
cerebral  layers  fuse  with  one  another  and  in  the  center  of  the  fovea  with  the 
cone-granules,  forming  a  thin  layer  in  which  the  boundaries  of  the  individual 
strata  can  no  longer  be  recognized.  In  the  center  of  the  fovea  (fundus  fovea) 
the  neuroepithelial  layer  (cone-cells)  alone  is  present. 

A  diffuse  yellow  pigment  permeates  the  cerebral  layer,  but  is  absent  in  the 
neuro-epithelial  layer,  and  therefore  the  fundus  foveje  is  colorless. 

In  the  region  of  the  ora  serrata  a  rapid  diminution  in  the  retinal  layers 
takes  place.  Optic-fibers  and  ganglion-cells  disappear  before  reaching  the  ora 
serrata.  Of  the  visual  cells  the  rod- visual  cells  are  the  first  to  vanish  ;  the 
cone-visual   cells  are  still  preserved,  but  appear  to  be  deprived  of  their  outer 


THE    EVE    ANIJ    ITS    APPENDAGES.  249 

segments.  Then  the  outer  reticular  layer  is  lost,  so  that  the  outer  and  inner 
granular  layers  become  confluent,  and  finally,  the  inner  reticular  layer  ceases. 
The  radial  fibers  of  Miiller,  on  the  contrary,  persist  and  are  highly  developed. 
The  ora  serrata  is  frequently  the  seat  of  senile  change.  Commonly  vacuoles 
occur;  they  appear  first  in  the  outer  granule  layer,  and  may  extend  into  the 
central  layers. 

The  pars  ciliaris  retina  consists  of  a  simple  layer  of  slender  columnar 
cells,  which  gradually  originate  in  the  blended  inner  and  outer  granule 
layers.  These  cells  are  covered  on  their  centrally-directed  surface  by  a  cuticu- 
lar  membrane,  a  true  menibrana  limitans  interna,  which  is  not  present  in  the 
pars  optica  retina  ;  their  peripheral  surface  is  joined  to  pigmented  cells,  a 
continuation  of  the  pigmented  epithelium. 

The  pars  iridica  retina:,  the  jjigment  layer  of  the  iris,  has  been  described 
(p.  241). 

With  regard  to  the  connections  of  the  nenw/s  elements  of  the  retina. 
according  to  the  foregoing  de.scription  the  axis-cylinder  processes  of  the 
ganglion-cells  of  the  ganglion  of  the  ojjtic  nerve  (basal  optic  ganglion)  and  of 


Fig.  234. — Mrkidional  Section  of  thb  Ora  Sbkkata  and  the  Adiacent  Portion  of  the  Pars  Cili- 
aris Retin*  op  a  Woman  Sbvkntv-eight  Years  of  Age.  X  70.  I.  Pigmented  epithelium.  2.  Cones, 
minus  their  outer  segment.  3.  External  limiting  membrane.  4.  Outer  granule  layer.  5.  Outer  reticular 
layer.  6.  Inner  gr.inulc  layer.  7.  Inner  reticular  layer.  8.  Radial  fibers.  9.  Vacuole  in  the  retina.  At 
10  the  outer  and  inner  nuclear  layers  become  contluent  and  at  11  continuous  with  the  cells  of  the  pars  ciliaris 
retinje,    Techn.  No.  170*/. 

the  Stellate  cells  of  the  inner  granule  layer  are  the  centripetal  optic-fibers  ; 
while  the  centrifugal  nerve-fibers  terminate  in  free  endings  in  the  inner  granule 
layer.  The  ganglion-cells  of  the  ganglion  retinje  apparently  possess  no  axis- 
cylinder  processes ;  their  union  with  the  other  nervous  elements  is  effected  by 
means  of  the  nervous  tangles  in  the  two  reticular  layers  (Fig.  231).  It  has 
recently  been  positively  asserted  that  a  direct  connection  exists  between  the 
nervous  elements  of  the  retina,  established  by  broad  anastomoses  and  by  a  true 
network.  The  connection  with  the  visual  cells  is  effected  by  the  intraepithe- 
lial processes  of  the  cells  of  the  ganglion  retinae,  which  terminate  between 
(not  within)  the  visual  elements.  Physiologic  researches  make  it  highly 
probable  that  the  visual-cells  constitute  the  essential  percipient  part  of  the 
retina. 

THE  OPTIC  NERVE. 
The  optic  nerre,  in  its  entire  intraorbital  course,  is  enveloped  in  sheaths 
which  are  processes  of  the  cerebral   membranes.     Outermost   is  the  compact 
dural  sheath,  consisting  of  longitudinally-disposed  bundles  of  connective-tissue ; 


2SO 


HISTOLOGY. 


following  this  is  the  exceedingly  delicate  arachnoidal  sheath,  which  sends 
numerous  relatively  thick  connective-tissue  trabecule  inward  to  the  pial  sheath, 
while  the  union  with  the  dural  sheath  is  represented  by  a  few  delicate  fibers. 
Innermost  lies  the  pial  sheath,  which  closely  invests  the  optic  nerve  and  sends 
off  numerous  septa  between  the  individual  nerve-fiber  bundles.  These  septa 
are  connected  with  one  another  by  transverse  trabecule,  the  resultant  structure 
being  a  transverse  lattice-work. 

The  tissue  of  the  pial  sheath  does  not  penetrate  within  the  nerve-fiber  bun- 
dles, but  only  forms  an  outer  envelope  for  them.  The  nerve-fiber  bundles 
consist  of  medullated  fibers  without  a  neurilemma;  they  are  held  together  by 
many  neuroglia-cells  ("  mossy  "  cells).  At  the  entrance  of  the  optic-nerve  into 
the  eyeball  the  dural  sheath  passes  into  the  sclera,  the  arachnoidal  sheath,  at 


Centr  1  irtery 
F  bers  of  lam  ni  cr  broba        [     Central  > 


'l*      \ 


Arachnoidal  sheath 


HHiiiiim^"' 


Fig.  235. — Longitudinal  Section  of  Optic  Entranxk  of  Human  Eye.  X  15.  Above  the  lamina  cribrosa 
the  narrowing  of  the  optic  nerve  is  visible.  The  central  artery  and  vein  have  been  for  the  most  part  cut 
longitndinally,  but  above  at  several  points,  transversely.     Techn.  No.  169  rf. 


its  anterior  border,  breaks  up  into  fibers,  so  that  the  subdural  space  lying  to  its 
outer  side  communicates  with  the  subarachnoidal  space  on  its  inner  side.  The 
pial  sheath  blends  with  the  sclera,  which  here  is  pierced  with  numerous  aper- 
tures for  the  nerve-fibers  passing  through  it  ;  this  portion  of  the  sheath  is  called 
lamina  cribrosa.  The  choroid  also  participates,  though  in  a  slight  degree,  in 
the  formation  of  the  lamina  cribrosa.  The  nerve-fibers  lose  their  medullary 
sheaths  at  the  point  of  entrance,  and  consequently  the  nerve  becomes  consid- 
erably reduced  in  size. 

In  the  distal  half  of  the  optic  nerve,  the  central  artery  and  vein  of  the 
retina  lie  in  its  axis  ;  the  connective-tissue  investing  these  vessels  is  connected  at 
many  points  with  the  pial  sheath,  as  well  as  with  the  lamina  cribrosa. 


THE    EYE    AND    ITS    APPENDAGES. 


251 


THE  LENS. 

The  crystalline  lens  consists  of  a  substantia  propria  which  on  its  anterior 
surface  is  covered  by  the  epithelium  of  the  lens  ;  the  whole  is  enveloped  by 
the  lens-capsule. 

In  the  substantia  pi-opria  a  soft  cortical  substance  and  a  firm  core  may 
be  distinguished  ;  it  consists  throughout  of 
colossal,  greatly-elongated  epithelial-cells, 
the  li'iis-fibcrs.  They  have  the  form  of  six- 
sided  prismatic  bands,  which  are  thickened 
at  their  posterior  extremities.  The  lens-fibers 
of  the  cortical  zone  have  smooth  borders, 
and  in  the  vicinity  of  the  equator  lies  an 
oval  nucleus.  The  lens-fibers  of  the  central 
portion  of  the  lens  have  dentated  outlines 
and  are  without  nuclei.  .\11  the  fibers  are 
united  and  held  together  by  a  small  amount 
of  cement-substance,  which  is  accumulated 
in  larger  quantities  at  the  anterior  and  pos- 
terior poles  of  the  lens  and  produces  the 
so-called  anterior  and  posterior  lens-stars, 
stellate  forms  seen  in  macerated  prepara- 
tions. All  the  lens-fibers,  beginning  at 
the  anterior  lens-star,  run  in  a  meridional 

direction  to  the  posterior  lens-star;  but  no  lens-fiber  spans  the  entire  half  of 
the  lens  ;  the  nearer  the  fibers  arise  to  the  anterior  pole,  the  more  remote  from 
the  posterior  pole  do  they  find  their  termination. 


IG.    236.-LENS-F1BEKS 

OF     AN    Ivp 

ANT.      A. 

Isolated  lens-fibers,  thi 

ree  with  sm 

00th,  one 

with   dcnt.ttcd   border? 

■■■     X  240. 

Tcchn. 

No.  178.     B.     Human 

lens-fibers 

cut  irans- 

versely ;     f ,   section   through     club-shaped 

ends.     X  560.     TechD. 

No.  179. 

;.  337. — Capsulr  and  Epithblii'M  op  Adult  Human  Lbns.  C  Inner  aspect. 
180  a.  D.  Lateral  aspect,  from  a  meridional  section  through  the  equator  of  the  lens 
Hum  :  3,  lens-fibers.     X  240.    Techn.  No.  180  d. 


X    240.     Techn,     No 
/,  capsule  :  2,  epithe 


The  leiis-epitlieliiiiii  consists  of  a  simple  layer  of  cubical  cells,  which  covers 
the  anterior  surface  of  the  lens  and  extends  as  far  as  the  equator  ;    here  the 


252  HISTOLOGY. 

epithelium,  by  gradual  elongation  of  its  elements,  becomes  transformed  into  the 
lens-fibers  (Fig.  237,  D). 

The  lens-capsule  is  a  transparent,  glassy,  elastic  membrane  ;  the  anterior 
capsule,  the  portion  covering  the  anterior  surface  of  the  lens,  is  1 1  to  1 5  /j  thick, 
the  corresponding  posterior  portion,  the  posterior  capsule,  only  5  to  7  ,a.  The 
lens-capsule  comprises  two  genetically  distinct  parts ;  the  one  is  a  cuticular 
formation,  a  product  of  the  epithelium  of  the  lens,  the  other,  of  the  nature 
of  connective  tissue,  is  a  transformation  product  of  the  embryonal  connective- 
tissue  sheaths. 

THE  VITREOUS  BODY. 
The  vitreous  hody  consists  of  a  fluid  substance — the  vitreous  sul'staiice — 
and  oi  Jitters  which  extend  in  all  directions  through  the  former.  The  surface 
of  the  vitreous  body  is  covered  by  a  somewhat  firmer  membrane,  the  hyaloid 
membrane,  and  in  certain  localities  contains  a  limited  number  of  fibrillse  and  a 
few  cells ;  of  the  latter  two  forms  may  be  distinguished,  round  elements, 
resembling  leucocytes,  and  stellate  or  fusiform  cells.  Cells  containing  clear 
vacuoles  are  probably  degenerating  forms. 

THE  SUSPENSORY  LIGAMENT. 
The  suspcnsoiy  ligament  (zonula  ciliaris,  zone  of  Zinn),  consists  of  deli- 
cate homogeneous  fibers  which  extend  from  the  surface  of  the  hyaloid  mem- 
brane, in  the  vicinity  of  the  era  serrata,  in  a  meridional  direction  toward  the 
lens.  They  are  attached  to  the  inner  surface  of  the  ciliary  processes  and  extend 
from  the  apices  of  the  same  over  to  the  equator  of  the  lens,  where  they  are 
attached  to  the  anterior  and  posterior  surfaces  and  to  the  equator  of  the  lens- 
capsule.  The  fibers  do  not  form  a  continuous  membrane,  but  are  radially 
plicated  e.xtensions  of  the  hyaloid  membrane  that  find  attachment  and  support 
on  the  lens.  The  annular  cleft  between  the  zonula  ciliaris  behind  and  the 
vitreous  body  in  front  is  designated  canal  of  Petit.  Other  authors  describe  the 
triangular  space  included  between  the  anterior  and  posterior  zonula  fibers  and 
the  lens-capsule  as  the  canal  of  Petit.  The  canal  is  not  completely  closed  on 
the  side  toward  the  posterior  chamber  of  the  eye. 

THE  BLOOD-VESSELS  OF  THE  EYEB.\LL. 

The  blood-vessels  of  the  eyeball  are  separated  in  two  sharply-defined 
regions,  which  are  in  communication  only  at  the  entrance  of  the  optic  nerve. 

Territoiy  of  the  Vasa  Centralia  Retina. — The  central  arteiy  of  the  retina, 
at  a  distance  of  15  to  20  mm.  from  the  eyeball,  enters  the  axis  of  the  optic 
nerve  and  runs  within  it  to  the  surface  of  the  optic  entrance.  Here  it  divides 
into  two  main  branches,  of  which  the  one  is  directed  upward,  the  other  down- 
ward, each  of  which  subdivides  and  supplies  the  entire  pars  optica  retinae 
to  the  ora  serrata.  During  its  course  in  the  optic  nerve  the  artery  gives  ofif 
numerous  small  branches,  which  run  within  the  processes  of  the  pial  sheath 


THE    EYE    AND    ITS    APPENDAGES.  253 

between  the  nerve-fiber  bundles,  and  anastomose  with  small  arteries  that  have 
entered  the  sheath  of  the  nerve  from  the  surrounding  adipose  tissue  and  also 
with  twigs  from  the  short  ciliary  arteries.  In  the  retina  itself  the  artery  breaks 
up  into  capillaries,  which  extend  into  the  outer  reticular  layer.  The  cerebral 
layer  of  the  retina  alone  contains  blood-vessels;  in  the  fundus  foveje  the  cere- 
bral layer  is  wanting,  and  with  it  the  blood-vessels.  The  veins  proceeding 
from  the  capillaries  run  parallel  with  the  branches  of  the  arteries  and  finally 
unite  in  the  vena  centralis  retina;  enclosed  within  the  axis  of  the  optic  nerve 
(Fig.  238). 

In  the  embryo  a  twig  from  the  central  artery  of  the  retina,  the  hyaloid 
artery,  passes  through  the  vitreous  body  to  the  posterior  surface  of  the  lens. 
This  artery  atrophies  before  birth,  but  the  canal  which  transmits  it  may  still  be 
found  in  the  vitreous  body  of  the  adult ;    it  is  called  the  hyaloid  canal. 

Territory  of  the  Vasa  Ciliaria. — This  region  is  characterized  by  the  com- 
plementary veins  taking  a  course  entirely  different  from  that  of  the  arteries. 

Of  the  arteries,  the  short  ciliary  arteries  supply  the  smooth  portion  of  the 
choroid,  while  the  long  ciliary  arteries  and  the  anterior  ciliary  arteries  are  des- 
tined chiefly  for  the  ciliary  body  and  the  iris. 

The  branches,  about  twenty,  of  the  short  ciliary  arteries  penetrate  the 
sclera  in  the  vicinity  of  the  optic  entrance;  after  giving  off  twigs  which  sup- 
|)ly  the  posterior  half  of  the  surface  of  the  sclera,  the  arteries  break  up  into  a 
narrow-meshed  capillary  network,  the  choriocapillaris.  At  the  optic  entrance 
the  arteries  anastomose  with  branches  of  the  arteria  centralis  retinse  and  there 
form  the  circular  artery  of  the  optic  nenie  ;  at  the  ora  serrata  they  anastomose 
with  recurrent  twigs  of  the  long  ciliary  and  the  anterior  ciliary  arteries. 

The  two  lon^  ciliary  arteries  likewise  penetrate  the  sclera  at  the  optic 
entrance  ;  the  one  artery  passes  to  the  nasal,  the  other  to  the  temporal  side  of 
the  eyeball  between  the  choroid  and  the  sclera  to  the  ciliary  body,  where  each 
artery  divides  in  two  diverging  branches  running  along  the  ciliary  margin  of 
the  iris ;  by  the  anastomoses  of  the  branches  of  the  two  arteries  a  vascular 
ring  is  formed,  the  larger  arterial  circle  of  the  iris  (circulus  iridis  major)  from 
which  numerous  twigs  are  given  off  to  the  ciliary  processes  and  the  iris.  Near 
the  pupillary  margin  of  the  iris  the  arteries  form  an  incomplete  ring,  the  smaller 
arterial  circle  (circulus  iridis  minor). 

The  anterior  ciliary  arteries  come  from  the  arteries  supplying  the  recti 
muscles  of  the  eye,  penetrate  the  sclera  near  the  corneal  margin,  communicate 
with  the  larger  arterial  circle  of  the  iris,  supply  the  ciliary  muscle,  and  send  recur- 
rent branches  to  unite  with  the  choriocapillaris.  Before  the  anterior  ciliary 
arteries  penetrate  the  sclera,  they  give  off  twigs  behind  for  the  anterior  half  of 
the  sclera,  and  in  front  to  the  conjunctival  sclera  and  to  the  corneal  limbus. 
The  cornea  itself  is  without  blood-vessels ;  only  at  the  margin,  in  the  anterior 
lamellce  of  the  substantia  propria,  is  there  a  circumferential  network  of  capillary 
loops. 

The  veins  all  run  toward  the  equator,  where  they  converge  to  four  (more 
rarely  five  or  six  )  small  stems,  the  whorl  veins  or  vence  vorticosce,  which  forth- 


354 


HISTOLOGY. 


with  pierce  the  sclera  and  empty  into  one  of  the  ophthahnic  veins.  In  addition 
to  these  there  are  small  complemental  veins  that  run  parallel  to  the  short  ciliary 
arteries  and  the  anterior  ciliary  arteries  ;  the  anterior  ciliary  veins  receive  twigs 


Vessels  op  the  Eye,  accoeding  to  Leber.  External  tunic  stippled,  middle 
ernal  tunic  and  optic  nerve  dotted  crosswise.  Arteries  light.  Veins  dark.  Region  of  the 
central  vessels  of  the  retina  (small  Italic  letters)  :  a.  Artery  :  a',  central  vein  of  retina :  i,  anastomosis 
with  vessels  of  the  sheath  ;  c,  anastomosis  with  branches  of  the  posterior  short  ciliary  arteries  :  d,  anasto- 
mosis with  choroidal  vessels.  Region  of  the  vessels  of  the  sheath  (large  Italic  letters):  A.  Inner;  B, 
outer  vessels  of  the  sheath.  Region  of  the  posterior  short  ciliary  vessels  (Italic  numerals):  /.  Arteries: 
/',  veins  (short  posterior  ciliarj):  //.  episcleral  arterial:  //',  episcleral  venous  branches  of  the  same;  ///, 
capillaries  of  the  choriocapillaris.  Region  of  the  posterior  long  ciliary  vessels  (.Arabic  numerals):  i.  Pos- 
terior long  ciliary  arterj';  2,  circulus  iridis  major  cut  transversely:  3.  branches  to  the  ciliary  body:  4, 
branches  to  the  iris.  Region  of  the  anterior  ciliary  vessels  (Greek  letters) :  a.  Artery  :  a',  vein  (anterior 
ciliary):  3,  connection  with  the  circulus  iridis  major; 
6',  venous  episcleral  branches:  e,  arterial;  e',  venous  brai 
venous  branches  to  the  corneal  limbus  ;    V,  vena  vorticosa ; 


Fig.  238. — Scheme  ' 


th  the  chori 
to  the  scleral  conjunctii 
3ss-section  of  the  venous 


from  the  ciliary  muscle,  from  the  episcleral  vascular  network,  from  the  con- 
junctival sclera,  and  from  the  circumferential  capillary  loops  of  the  cornea. 
The  episcleral  veins  communicate    with  the  vena;   vorticos?e   at   the   equator. 


THE    EVE    AND    ITS    APPENDAGES.  255 

The  anterior  ciliary  veins  eventually  communicate  also  with  the  canal  of 
Schlemm.  This  canal  is  an  annular  cleft  encircling  the  cornea,  but  lying 
just  within  the  sclera.  It  is  by  some  regarded  as  a  lymph-space  in  open  com- 
munication with  the  anterior  chamber,  by  others  held  to  be  a  venous  channel. 

THE  LYMPH-CHANNELS  OF  THE  EYEBALL. 
The  eye  possesses  no  proper  lymph-vessels,  but  a  series  of  intercommuni- 
cating lymph-spaces.     Two  complexes  of  such  spaces  may  be  distinguished,  an 
anterior  and  a  posterior  tract.     The  anterior  tract  comprises  : — 

1.  The  lymph-canalkuli  of  the  cornea  and  sclera. 

2.  The  anterior  chamber  of  the  eye,  which,  with  Schlemm's  canal,  by 
means  of  the  capillary  clefts  between  the  iris  and  the  lens,  communicates 
with — 

3.  The  /'os/ericr  c/iamfier  of  the  eye.  The  latter  is  in  open  connection 
with — 

4.  The  canal  of  Petit. 

The  last  three  spaces  stand  in  close  relation  to  one  another,  and  may  be 
injected  from  the  anterior  chamber. 
The  posterior  tract  includes: — 

1 .  The  hyaloid  canal. 

2.  The  lymph-clefts  between  the  sheaths  of  the  optic  nen-e  (the  subdural 
and  the  subarachnoidal  spaces),  the  narrow  cleft  between  the  choroid  and  the 
sclera — the  perichoroidal  space — and  Tenon's  space,  which  extends  from  the 
dural  sheath  of  the  optic  nerve  to  the  optic  foramen.  These  spaces  may  be 
filled  from  the  subarachnoidal  space  of  the  brain.  The  contents  of  these  spaces 
is  a  filtrate  from  the  blood-vessels,  which  also  permeates  the  vitreous  body.  The 
quantity  of  this  fluid  in  the  perichoroidal  space,  also  in  Tenon's  space,  is 
normally  exceedingly  scanty.  Both  these  spaces  serve  to  facilitate  the  move- 
ments of  the  choroid  and  of  the  eyeball,  and  may  be  regarded  as  synovial  spaces. 

THE  NERYES  OF  THE  EYEBALL. 
The  nerves  of  the  eyeball  penetrate  the  sclera  in  the  vicinity  of  the 
entrance  of  the  optic  nerve  and  run  forward  between  the  outer  tunic  and  the 
choroid  ;  after  giving  off  bundles  accompanied  by  ganglion-cells  to  the  choroid, 
they  form  an  annular  plexus  intermingled  with  ganglion-cells  lying  upon  the 
ciliary  body — the  ciliary  ganglionic ple.xiis  (orbiculus  gangliosus  ciliaris),  from 
which  branches  go  to  the  ciliary  body,  the  iris,  and  the  cornea.  The  nerves  of 
the  ciliary  boiiv  terminate  in  delicate  pointed  ends  in  the  blood-ves.sels,  in  the 
ciliary  muscle  between  the  muscle-bundles  in  the  form  of  branched  ends,  which 
perhaps  subserve  the  muscular  sense,  and  on  the  scleral  surface  of  the  ciliary 
body  in  the  form  of  a  delicate  plexus.  The  medullated  nerves  of  the  iris  form  net- 
works and  lose  their  medullary  sheath  as  they  pass  to  the  pupillary  margin  :  their 
terminal  ramifications  are  in  part  distributed  to  the  smooth  muscle-fibers  and  the 
blood-ves-sel  walls  ;    another  jjortion    forms  a  dense  sensory  plexus  lying  close 


256  HISTOLOGY. 

beneath  the  anterior  iridal  surface.  The  nerves  to  the  cornea  first  enter  the  sclera 
and  form  a  circular  plexus — plexus  aniiiilaiis — surrounding  the  corneal  margin, 
from  which  branches  are  distributed  to  the  sclera  and  to  the  cornea.  In  man 
the  twigs  in  the  sclera  terminate  in  spherical  end-bulbs  lying  close  under  the 
epithelium;  they  are  also  found  in  the  substance  proper  of  the  cornea  for  a 
distance  of  from  i  to  2  mm.  within  the  corneal  limbus.  The  branches  that  go 
to  the  cornea,  after  their  entrance  in  the  substance  proper  lose  their  medullary 
sheath  and  as  naked  a.xis-cylinders  penetrate  the  entire  structure.  They 
form  networks,  which,  according  to  the  plane  they  occupy,  are  described  as — 
the  stroma  or  gnnitid-J'/exus,  which  lies  in  the  deeper  strata  of  the  cornea;  the 
siil'hasilar  plexus,  situated  beneath  the  anterior  basal  membrane  ;  the  sub- 
epithelial plexus,  lying  close  under  the  epithelium.  From  the  latter  plexus 
exquisitely-delicate  nerve-fibrillse  pass  up  into  the  epithelium  between  its 
elements,  and  form  the  exceedingly  fine  intraepithelial  plexus,  whose  naked 
axis-cylinders  terminate  in  free  ends  between  the  epithelial  cells  (Fig.  239). 


-^r 


Fig.  239. — From  a  Vertical  Section  through  the  Human  Cornea.  X  240. 
penetrating  the  anterior  basal  membrane  ;  s,  subepithelial  plexus  beneath  the 
the  intraepithelial  plexus  ascending  betweett  the  epithelial  cells.     Techn,  No.  1 


I  propria. ^^__^^^ 


THE  EYELIDS. 

The  eyelids  are  folds  of  the  integument,  which  enclose  muscles,  loose  and 
compact  connective  tissue,  and  glands.  The  outer  fold  of  the  eyelid  retains 
the  usual  characteristics  of  the  skin ;  the  inner  fold,  that  toward  the  eye,  is 
considerably  modified  and  is  called  \k\R  palpebral  conjunctiva.  The  skin  on  the 
external  surface  of  the  eyelid  extends  over  the  lower  free  margin  and  does  not 
pass  into  the  palpebral  conjunctiva  until  it  reaches  the  posterior  border, /a^f/'z-i?/ 
bonier. 

The  eyelid  is  best  studied  in  a  sagittal  section,  in  which,  counting  from 
before  backward,  the  following  strata  are  found  : — 

I.  The ////'<'^'v////<v/;' is  thin  and  beset  with  fine  hairs ;  in  the  corium  small 
sweat-glands  are  found,  also  pigmented  connective-tissue  cells  ;  the  latter  are  of 
rare  occurrence  in  the  corium  elsewhere.  The  subcutaneous  tissue  is  very  loose, 
rich  in  fine  elastic  fibers,  and  contains  but  few  fat-cells,  which  may  be  entirely 
wanting.  Near  the  border  of  the  lid  the  corium  is  more  compact  and  beset 
with  more  conspicuous  papillae.  At  the  anterior  edge  of  the  margin  of  the  lid 
two  to  three  rows  of  robust  hairs,  the  cilia,  extend  obliquely  outward  ;  their 
follicles  are  deeply  implanted  in  the  corium.     The  cilia  undergo  rapid  shed- 


THE    EVE    AND    ITS    APPENDAGES. 


257 


ding  ;  their  length  of  life  is  said  to  be  about  from  100  to  150  days ;  as  a  result, 
hairs  in  all  stages  of  development  are  frequently  found  in  the  eyelashes.  The 
hair-follicles  of  the  cilia  are  provided  with  small  sebaceous  glands,  and  take 
up  the  e.xcretory  ducts  of  the  so-called  MolT s  glands,  which  in  their  minute 
structure  resemble  coil-glands,  and  differ  from  these  only  in  that  their  lower 
ends  are  less  convoluted. 

2.  Posterior  to  the  subcutaneous  tissue  lie  transverse  bundles  of  cross- 
striated  muscle-fibers  of  the  orbicularis  palpebrarum  ;  the  portion  of  the  muscle 
lying  behind  the  cilia  is  named  the  ciliary  or  marginal  muscle. 


Sr   C  E 


;.  240.— jAciiTAL  SRcri/.s  OF  THB  Uppbr  Eyblid  of  A  Six-.Mosths'-Old  Child.  X  lo.  i.  Intcgu 
ment:  £",  epidermis  ;  C,  corium  ;  .Si-,  subcutaneous  tissue ;  //i^.  hair-follicle  of  lanugo  hair:  A",  coil-gland 
M^t  eyelash,  with  the  aiilage  of  a  new  hair  {Eh\ ;  /*",  W" ,  portions  of  follicles  of  eyelashes  ;  M,  portion  of  3 
gland  of  .Moll.  2.  Region'of  the  orbicularis  palpebrarum  muscle  ;  O.  bundles  of  this  muscle  cut  transversely 
McR,\\A  muscle.  3.  Expanded  tendon  of  the  levator  palpebrarum  superior:  mps,  superior  palpebrarum 
muscle.  4.  Conjunctival  portion  :  e,  conjunctival  epithelium :  tp,  tunica  propria  :  at,  accessor^'  tear-glands 
/,  tarsus  :  m.  Meibomian  glands,  the  mouth  of  the  excretory  duct  is  not  visible:  a,  transverse  section  of 
the  arcus  tarseus  ;  a' ,  transvcr^ie  section  of  the  arcus  tarseus  extemus.  5,  Margin  of  eyelid.    Techn.  No.  l8j. 


3.  Behind  the  muscle  the  fibrous  extensions  of  the  tendon  of  the  levator 
palpebra  are  met,  which  are  partly  lost  in  the  areolar  tissue  present — the  fa.scia 
palpebralis, — and  partly  attached  to  the  upper  margin  of  the  tarsus  ;  the  latter 
contain  smooth  muscle-fibers,  the  lid-muscle  of  Midler.  In  the  lower  eyelid 
the  expansion  of  the  tendon  of  the  inferior  rectus  muscle  contains  bundles  of 
nonstriped  muscle-fibers. 


258  HISTOLOGY. 

4.  The  farsiis  is  a  plate  of  dense  fibrous  tissue,  which  gives  firmness  and 
support  to  the  eyelid.  It  lies  immediately  in  front  of  the  conjunctiva,  to  which 
it  belongs,  and  occupies  the  entire  lower  two-thirds  of  the  height  of  the  eyelid. 
In  its  substance  the  Meibomian  glands  are  embedded,  elongated  bodies 
which  consist  of  a  wide  excretory  duct,  opening  on  the  palpebral  border,  and  of 
short  acini.  In  their  histology  the  Meibomian  glands  agree  with  the  sebaceous 
glands.  At  the  upper  edge  of  the  tarsus  lie  branched  tubular  glands,  in  part 
enclosed  by  its  substance,  which  in  their  minute  structure  coincide  with  the 
tear-glands,  and  therefore  are  called  accessory  tear-glands ;  they  occur  princi- 
pally in  the  inner  (nasal)  half  of  the  eyelid. 

Behind  the  tarsus  lies  the  conjtinctiva  proper,  which  consists  of  an  ejiithe- 
lium  and  a  tunica  propria.  The  former  is  a  stratified  columnar  epithelium, 
with  several  rows  of  spherical  cells  in  the  deeper  portion  and  a  row  of  mainly 
short  cylindrical  cells  on  the  surface.  The  latter  possess  a  narrow  hyaline 
cuticular  border.  Goblet-cells  also  occur  in  varying  numbers.  At  the  palpebral 
border  the  epithelium  passes  gradually  into  the  stratified  scaly  variety,  which 
occasionally  extends  far  over  on  the  conjunctiva.  The  lower  portion  of  the 
palpebral  conjunctiva  is  smooth.  In  the  upper  portion,  on  the  contrary,  the 
epithelium  forms  irregular  pocket-like  depressions,  which  differ  greatly  in  indir 
vidual  development  and  in  sections,  when  highly  developed,  resemble  glands. 
The  tunica  propria  of  the  conjunctiva  consists  of  fibrous  tissue,  plasma-cells, 
in  varying  number,  and  of  lymphoid  cells,  whose  number  likewise  varies 
greatly.  In  animals,  especially  in  ruminants,  the  latter  form  true  nodules, 
the  so-called  trachoma  glands,  from  the  summit  of  which  the  leucocytes 
wander  through  the  epithelium  to  the  surface ;  in  man,  the  migration  of  the 
leucocytes  occurs  in  a  slighter  degree.  In  the  region  of  the  conjunctival 
recesses,  the  tunica  propria  is  divided  into  pajiill^  by  the  depressions  of  the 
epithelium. 

The  palpebral  conjunctiva  passes  from  the  eyelid  to  the  eyeball,  the  ante- 
rior surface  of  which  it  covers.  At  the  line  of  transition,  the  fornix  conjunc- 
tiva:, a  loose  sub-conjunctival  tissue  occurs  under  the  tunica  propria.  The 
epithelium  is  the  same  as  that  on  the  lid  ;  the  tunica  propria  contains  fewer  leuco- 
cytes, but  possesses  normally  about  twenty  small  lymph-nodules  and  a  few 
mucous  glands.  On  the  scleral  conjunctiva  the  stratified  columnar  epithelium, 
within  a  certain  distance  of  the  cornea,  becomes  transformed  into  the  stratified 
scaly  variety,  which  continues  over  the  cornea. 

The  rudimentary  third  eyelid  (plica  semilunaris)  consists  of  connective 
tissue  and  stratified  squamous  epithelium.  The  cariincula  lacrymalis  resemble 
the  skin  in  structure — with  the  exception  that  the  stratum  corneum  is  absent — 
and  contain  fine  hairs,  sebaceous  glands,  and  accessory  tear-glands. 

The  blood-vessels  of  the  eyelids  pass  from  the  outer  and  inner  angles,  and 
form  an  arch,  the  anus  tarsens,  at  the  margin  of  the  lid,  and  a  second  arch, 
the  arci/s  tarseus  externus,  at  the  upper  edge  of  the  tarsus.  Branches  from 
these  arches  ramify  in  the  skin,  surround  the  glands  of  Meibom,  penetrate  the 
tarsus,  and   form  a  capillary  network  Iving   beneath   the   conjunctival   epithe- 


THE    EYE    AND    ITS    APPENDAGES. 


259 


Hum  ;  they  also  supply  the  fornix  conjunctivae,  the  scleral  conjunctiva,  and 
anastomose  with  the  anterior  ciliary  arteries. 

The  lymph-vessels  form  a  close-meshed  network  in  the  tarsal  conjunctiva, 
a  very  open-meshed  network  on  the  anterior  surface  of  the  tarsus.  According 
to  some  authors,  the  lymph-channels  of  the  scleral  conjunctiva  are  closed  at 
the  corneal  limbus ;  according  to  others,  they  send  minute  canaliculi  into  the 
tissue  of  the  cornea,  and  are  thus  in  communication  with  the  system  of  lymph- 
spaces  and  canaliculi  in  the  latter. 

The  tienes  form  a  rich  plexus  at  the  margin  of  the  lid. 


•i«»\ 


«;v}s^''l^ 


'~*.Mf~ 


'zy 


Fig.  341. — From  a  Thin  Sbction  of  Human  Lacrymal  Gland.  X  340.  ^-  Gland:  <»,  tubule  cut  trans- 
verscly ;  a',  group  of  tubules,  mostly  cut  obliquely,  the  lumen  of  one  tubule  only  visible  below ;  s,  inter- 
caiatcd  tubule  with  cubical  (above  to  the  left),  flat  (below  to  the  right),  epithelial  cells  :  y,  intercalated  tubule 
in  cross-section,  lined  with  moderately  high  cylindrical  cells  ;  d,  connective  tissue.  B.  Cross-section  of  the 
duct :  e,  double  layer  of  cylindrical  epithelium  ;  6,  connective  tissue.     Techn.  No.  183. 


THE  LACRYMAL  GLANDS. 

The  lacrymal  glands  are  compound  tubular  glands,  provided  with  several 
excretory  ducts.  The  latter  are  clothed  with  a  two-layered  cylindrical  epi- 
thelium, and  pass  into  long  narrow  intercalated  tubules  clothed  with  low 
ejMthelial  cells.  These  pass  into  the  gland-tubules,  which  are  lined  by  serous 
gland-cells. 

The  walls  of  the  laoymal  canaliculi  consist  of  stratified  scaly  epithelium 
and  for  the  greater  part  of  longitudinally-disposed  cross-striped  muscle-fibers. 
The  tunica  propria  is -rich  in  elastic  fibers  and,  beneath  the  epithelium,  in 
cellular  elements. 

The  lacrymal  sac  and  the  naso-lacrymal  duct  are  comi)osed  of  a  two-lay- 
ered columnar  epithelium  ;  the  tunica  propria  is  chiefly  adenoid  in  character, 
and  is  separated  from  the  underlying  periosteum  by  a  dense  plexus  of  veins. 


XI.  THE   ORGAN   OF   HEARING. 

The  organ  of  hearing  consists  of  three  divisions:  the  innermost,  the  in- 
ternal ear,  which  encloses  the  end -apparatus  of  the  auditory  nerve  ;  the  other 
divisions,  middle  ear  and  external  ear,  are  only  accessory  apparatus. 

THE  INTERNAL  EAR. 
The  internal  ear  consists  of  two  membranous  saccules  that  communicate 
with  each  other  by  means  of  a  minute  canal,  the  ductus  endolytnphaficus.  The 
one  saccule,  the  utricle,  is  in  connection  with  membranous  tubules,  the  semi- 
circular canals,  each  of  which  at  the  point  where  it  opens  in  the  utricle  pos- 
sesses a  dilatation,  the  ampulla.  The  other  saccule,  the  sacculus,  connects 
with  a  long  spirally-wound  membranous  duct,  the  cochlea. 

The  sacculus  and  utriculus,  the  semicircular  canals  and  the  membranous 
cochlea  constitute  the  membranous  labyrinth.  This  is 
enclosed  within  the  sphenoid,  in  a  space  having  similar 
outlines,  the  bony  labyrinth,  which  it  does  not  completely 
fill.  The  unfilled  space  is  occupied  by  a  watery  fluid, 
the  perilymph.  A  similar  fluid,  the  endolymph,  is  found 
within  the  interior  of  the  membranous  labyrinth. 

The  saccules  and  the  semicircular  canals  exhibit 
the  same  structure,  but  the  cochlea  is  essentially  different, 
so  that  it  requires  a  separate  description. 
The  Saccule,  the  Utricle,  and  the  Semicircular  Canals. — Their  walls 
comprise  three  layers.  The  outermost  is  a  connective-tissue  layer  rich 
in  elastic  fibers;  this  is  followed  within  by  a  delicate  basement  membrane 
beset  with  minute  excrescences,  which  is  covered  on  its  inner  surface  by  a  sim- 
ple squamous  epithelium.  This  simple  structure  undergoes  alteration  at  the 
positions  where  the  filaments  of  the  auditory  nerve  are  received,  the  macuhe 
cribrosce  of  the  saccule  and  utricle,  the  cristm  acusticce  on  the  ampullse  of  the 
semicircular  canals.  The  connective  tissue  and  basement  membrane  become 
thicker  here  ;  the  squamous  epithelium  in  the  vicinity  of  the  maculas  and  cristas 
becomes  transformed  into  columnar  epithelium  wdth  a  cuticular  border,  and 
passes  into  the  neuro-epithelium  of  the  macute  and  cristas.  The  neuro- 
epithelium  is  likewise  a  simple  layer,  and  consists  of  two  kinds  of  cells : 
(i)  fiber-cells,  elongated  elements  that  occupy  the  entire  depth  of  the  epithe- 
lium, are  slightly  expanded  at  the  upper  as  w-ell  as  at  the  lower  end,  and  con- 
tain an  oval  nucleus  ;  they  are  the  sustentacular  elements  ;   (2)  hair-cells,  cylin- 

260 


a> 

;.  242 

.-Otolith 

lechn 

THE    Saccui.u 

iNPANT.       X56C 

.  No.  184 

THE    ORGAN    OF    HEARING.  261 

drical  elements  occupying  only  the  upper  half  of  the  thickness  of  the  epithe- 
lium, which  in  the  lower  rounded  portion  contain  a  spherical  nucleus  and 
bear  on  their  free  surface  a  bundle  of  long,  delicate  agglutinated  filaments,  the 
"auditory  hairs."  The  hair-cells  are  the  terminal  apparatus  of  the  auditory 
nerve.  The  nerve-fibers  lose  their  medullary  sheaths  on  entering  the  epithe- 
lium, divide,  and  ascend  to  the  base  of  the  hair-cells  as  naked  axis-cylinders 
where  each  fiber  divides  into  three  to  four  varicose  twigs,  which  run  be- 
neath several  hair-cells  parallel  to  the  surface  of  the  epithelium,  and  finally 
turn  upward  and  terminate  in  contact  with  the  lateral  surface  of  a  hair-cell  in 
a  free  pointed  end.=*=  During  their  horizontal  course  they  send  upward  a  few 
twigs,  which  end  in  the  same  manner  in  contact  with  the  hair-cells.  These 
ends  do  not  reach  to  the  surface  of  the  epithelium.  The  free  surface  of  the 
neuro-epithelium  is  covered  by  a  continuation  of  the  cuticular  zone,  which  is 
perforated  by  the  auditory  hairs.  The  maculae  acusticse  are  covered  by  a  soft, 
gelatinous  substance  (a  cuticula?),  in  which  innumerable  prismatic  crystals  of 
calcium  carbonate,  the  otoliths,  i  to  15  //  in  size,  are  embedded  ;  they  form  the 
otolith  meml>raiie.  On  the  crista  acusticK  the  so-called  cupola  occurs;  in  fresh 
])rei)arations  it  is  an  invisible  substance;  on  the  application  of  fixation  fluids 
it  coagulates  and  thus  becomes  visible. 

The  wall  of  the  bony  labyrinth  is  covered  by  a  thin  iieriosteum  and  flat- 
tened connective-tissue  cells.  The  saccules  and  semicircular  canals  are  secured 
to  the  walls  of  the  bony  labyrinth  by  means  of  connective-tissue  trabeculse. 


The  Cochlea. 
The  membranous  cochlea,  the  ductus  cochlearis,  does  not  entirely  fill  the 
space  within  the  bony  cochlea.  It  lies  with  one  wall  in  contact  with  the  outer 
wall  \  of  the  bony  cochlea ;  the  upper  or  vestibular  wall  (^membrane  of 
Reissner)  bounds  the  scala  vestibuli  ;  the  lower  or  tympanic  wall  {membran- 
ous spiral  lamina')  is  directed  toward  the  scala  tympani.  The  angle  in  which 
the  vestibular  and  tympanic  wall  meet  lies  on  the  free  end  of  the  osseous  spiral 
lamina.  There  the  periosteum  and  the  fibrous  coat  of  the  ductus  cochlearis 
are  especially  well  developed  and  form  a  prominence,  the  limbus,  which  rests 
with  a  broad  surface  on  the  bony  spiral  lamina,  slopes  upwards,  and  terminates  in 
a  sharp  edge.  This  edge  is  called  the  labium  vestibulare ;  the  free  margin  of  the 
bony  spiral  lamina  is  called  the  labium  tympanicum ;  between  the  labia  is  a 
recess,  iht  sulcus  spiralis  (Y\g.  249).  The  inner  surfaces  of  the  ductus  cochlearis 
are  covered  by  an  epithelium  that  varies  greatly  in  different  localities  ;  the  outer 
surfaces — toward  the  scala  vestibuli  and  scala  tympani — are  covered  by  a  deli- 


*  The  horizontal  branches  interlace  and  form  a  small,  but  direct  "  lattice- work,"  which  also 
in  other  methods  than  that  of  Golgi  appears  to  consist  of  a  Kiyer  of  strongly-refracting  granules. 
The  granules  are  the  varicosities  and  the  optical  cross-sections  of  the  horizontal  fibers. 

1 1  follow  here  the  customary  description,  in  which  the  cochlea  is  placed  in  such  a  manner 
that  the  base  is  directed  downward,  the  summit  upward;  accordingly,  "  inner "  is  toward  the 
axis  of  the  cochlea,  "  outer  "  toward  the  periphery. 


262 


HISTOLOGY. 


cate  continuation  of  the  periosteum  which  clothes  both  scalie.  On  the  outer 
wall  of  the  cochlea  the  periosteum  becomes  greatly  thickened,  and  in  cross- 
section  appears  as  a  crescentic  mass,  the  ligamenttim  spirale,  which  extends  both 
above  and  below  the  attached  surface  of  the  ductus  cochlearis. 

The  structure  of  the  outer  and  the  vestibular  wall  of  the  membranous 
cochlea  is  comparatively  simple,  that  of  the  tympanic  wall,  on  the  other  hand, 
is  extremely  complicated. 

The  outer  wall  and  the  spiral  ligament  together  consist  of  epithelium  and 
connective  tissue.  The  latter,  next  to  the  bone,  is  a  dense  fibrous  tissue  ;  this 
passes  into  a  loose  connective  tissue  which  contributes  the  chief  bulk  of  the 
spiral  ligament.  The  epithelium  is  composed  of  a  row  of  cubical  epithelial 
cells.  A  dense  network  of  blood-vessels,  the  stria  vascularis,  occupies  three- 
fourths   of   the  height  of  the  outer  cochlear  wall.     At  its  lower  end  a   vein 


Bony   axis  of  cochlea 
(modiolus). 


Organ  of  Corti  (organon 
spirale). 


[^ Outer  bony  wall  of 

^  cochlea. 

Vas  prominens. 

Ligamentum  spirale. 


Fig.  243. — Sfction  through 
contains  longitudinal  canal 
cochlea.  The  membrana  ^ 
tectoria  can  not  be  seen.     1 


THE  Second  Turn  of  the  Coch 
;  cut  obliquely,  j.  Bony  wall  betw 
estibularis  is  torn,  the  upper  fragn 
echn.  No.  1S6. 


nfant.  X  25.  The  modiolus 
nd  and  third  (half)  turns  of  the 
ned  upwards.      The  membrana 


projects  into  the  lumen  of  the  cochlea,  the  proiiiincntia  spiralis  (vas  promi- 
nens) (Fig.  243).  The  capillaries  of  the  stria  vascularis  lie  close  beneath  the 
epithelium  ;   they  are  the  source  of  the  endolymph. 

The  vestilnilar  wall  {Reissner' s  membrane),  consists  of  a  process  of  the 
periosteum  of  the  scala  vestibuli,  that  is  of  delicate  fibrous  tissue  and  flattened 
cells,  which  on  the  surface  turned  toward  the  ductus  cochlearis  is  clothed  with 
a  simple  layer  of  polygonal  epithelial  cells. 

The  tympanic  wall  consists  of  two  portions  :  the  limbiis,  with  the  free 
margin  of  the  bony  spiral  lamina,  and  Hn^  lamina  spiralis  membranacea. 

The  limbiis  consists  of  compact  connective  tissue,  containing  an  abundance 
of  spindle-shaped  cells,  which  below  is  continuous  with  the  tissue  of  the 
periosteum,  and  on  its   free  surface  is  beset  with  peculiarly-shaped  papillre. 


THE    ORGAN    OF    HEARING.  263 

They  have  the  form  of  an  irregular  hemisphere ;  toward  the  labium  vestibulare 
they  become  small  elongated  plates,  the  so-called  auditory  teeth,  which  lie  in  a 
single  row  next  to  one  another.  The  surface  of  the  limbus  is  covered  by  a 
simple  layer  of  flattened  epithelial  cells,  which  at  the  edge  of  the  labium  ves- 
til)ulare  passes  into  the  cubical  epithelium  of  the  sulcus  spiralis  (Fig.  247,  A). 

Labium  tympanicum. 


Labium  vcsttbutare. 


Zona  perforata. 
Auditory  teeth. 


k,  °C5ci>S:r=r=:3=*-    Papilla:. 

Pic.  244.— a  Surface  View  op  Lamina  Spiralis  op  Cat.  X  240.  The  vestibular  lamina  is  seen  from  above. 
Between  the  auditorj'  icelh  two  nuclei  of  the  epithelial  cells  are  visible.  On  the  left  of  the  picture  the  upper 
surface  of  the  auditory  teeth  is  in  focus,  on  the  right,  the  plane  of  the  zona  perforata.     Tcchn.  No.  185. 

The  upper  surface  of  the  free  margin  of  the  osseous  spiral  lamina  is  per- 
forated by  a  single  row  of  slit-like  openings,  the  foramina  nervina,  through 
which  the  nerves  enclosed  within  the  bony  lamina  emerge,  to  penetrate  within 
the  epithelium  of  the  basilar  membrane.  This  portion  of  the  osseous  spiral 
lamina  is  called  zona  perforata. 

The  membranous  spiral  lamina  comprises  :    ( i  )   the  memhrana  basilaris,  an 
extension  of  the  limbus  and  of  the  periosteum  of  the  osseous  spiral  lamina  :    (2) 
the  tympanic  lamella,  which  is  a  process  of  the  periosteum  of  the  scala  tympani 
and  clothes  the  lower  surface  of  the  basilar  membrane  ; 
and  (3)  the  epithelium   of  the  ductus  cochlearis,  which 
rests  upon  the  upi)er  surface  of  the  basilar  membrane. 

The  membraiia  basilaris  consists  of  a  structureless 
substance  which  contains  rigid,  perfectly  straight  fibers, 
extending  from  the  labium  tympanicum  to  the  spiral 
ligament,  and  also  oblong  nuclei.  The  membrane  has 
a  finely  striated  appearance  (Fig.  245,7"). 

The  tympanic  lamella  is  composed  of  a  delicate 
connective  tissue  containing  spindle-cells,  the  fibers  of 


which  are  dis[)0sed  vertically  to  the  elements  of  the  ^cttnata'"^*drawn'''°  wi"h 
basilar  membrane  (Fig.  245,  b).  fe'renf  e°pi,hei;::m  (cem  oi 

The  epithelium  of  that  half  of  the  membranous  S?£rU  in'foi!^:/"''^^ 
spiral  lamina  toward  the  axis  of  the  cochlea  is  differ-  f.iarisl'ibcirsTvEe  nil: 
entiated  as  the  highly-specialized  neuro-epithelium,  the  ti'^focLl'^' '^S"' No"'!^^ 
spiral  organ  (organ  of  Corti),  while  that  occupying  the 

outer  half,  toward  the  spiral  ligament,  consists  of  indifferent  epithelial  elements. 
The  spiral  lamina  is  therefore  divided  into  two  zones :  an  inner,  occupied  by 
the  spiral  organ,  zona  tecta — and  an  outer,  zona  pectinata — so  called  because 
of  the  striations  of  the  basilar  membrane  shimmering  through  it. 

The  most  remarkable  elements  of  the  spiral  organ  are  the  pillar-cells  or 
rods  of  Corti,  peculiarly-shaped  and  for  the  greater  part  rigid  forms,  arranged 


264  HISTOLOGY. 

in  two  rows  throughout  the  entire  length  of  the  cochlea  ;  an  inner  row,  the 
inner  pillars^  and  an  outer  row,  the  outer  pillars  (Fig.  247).  The  two  rows  of 
pillars  converge  and  form  an  arch,  the  arctis  spiralis,  which  spans  a  triangular 


Cells  of  Claud 
Fibe 


tympanicum.    -i 
vestibulare.        > 


Ganglion  spirale. 


Fig.  246. — Lamina  Spiralis  op  Cat  seen  prom  thi 

been  removed.  X  50.  to.  Lamina  spiralis  ossea,  inner  half  cleft  and  broken  at  s< 
spiral  ganglion  project  from  the  posterior  border  of  the  same.  hti.  Lamina  spiralis 
of  Claudius  have  partly  fallen  off,  so  that  the  fibers  of  the  membrana  basilaris  are 
tion.     Techn.  No.  1S5. 


:  membrana  tcctoria  has 
eral  points.  Cells  of  the 
nembranacea.  The  cells 
isible  as  a  delicate  stria- 


FiG.  247.— Scheme  of  the  Structure  op  the  Tympanic  Wall  of  the  Duct  of  the  Cochlea.  A.  Seen 
from  the  side.  B.  Seen  from  the  surface.  In  the  latter,  the  free  upper  surface  is  in  focus.  It  is  evident  that 
the  epithelium  of  the  sulcus  spirahs,  lying  in  other  planes,  as  well  as  the  cells  of  Claudius,  can  only  be 
distinctly  shown  by  depressing  the  tube.  The  membrana  tectoria  has  not  been  drawn.  The  spiral  nerve- 
fibers  are  indicated  by  dots. 


space,  the  tunnel,  the  base  of  which  is  directed  toward  the  basilar  membrane. 
The  tunnel  is  nothing  more  than  a  very  large  intercellular  space,  filled  with  a 
soft  mass,  the  intercellular  substance. 


THE    ORGAN    OF    HEARING.  265 

Regarding  the  histology  of  the  pillar-cells,  the  following  details  are  to  be 
considered  :  The  inner  pillar-cells  are  rigid  bands  in  which  a  three-sided  ex- 
panded base,  a  slender  body,  and  concave  head,  with  the  concavity  directed  out- 
ward, may  be  distinguished.  The  head  is  furnished  with  a  thin  process,  the 
"  head-plate  "  (Fig.  247).  The  body  and  base  of  the  cell  are  surrounded  by 
a  scant  amount  of  protoplasm,  which  only  to  the  outer  side  of  the  base,  in  the 
vicinity  of  the  nucleus,  is  present  in  somewhat  larger  amount.  The  outer  pil- 
lar-cells exhibit  the  same  details,  e.xcepting  that  the  portion  containing  the 
nucleus  lies  to  the  inner  side  of  the  base;  the  rounded  articular  head  rests  in 
the  concave  facet  of  the  head  of  the  inner  pillar-cells  ;  the  broader  head-plate  is 
covered  in  its  greater  part  by  the  head-plate  of  the  inner  pillars.  To  the  inner 
side  of  the  inner  pillars  lies  a  simple  row  of  cells,  the  inner  hair-cells,  short 
cylindrical  elements  that  do  not  extend  to  the  basilar  membrane  ;  they  possess 
a  rounded  base  and  about  twenty  stiff  hairs  on  their  free  surface.  To  the  inner 
side  of  the  inner  hair-cells  lies  the  cubical  epithelium  of  the  sulcus  spiralis.     On 


Fig.  348. — SuRFACB  Vibw  op  Lamina  Spiralis  Mbmbkanacea  op  Cat.  X  340.  A.  Outer  pillar-cells  :  k,  head- 
plates  of  the  same,  upper  surface  in  focus  ;  ap,  body  and  inferior  extremity  drawn  with  gradual  depression  of 
the  tube ;  ktp,  portions  of  the  head-plates  of  the  inner  pillar-cells.  B.  It.  Labium  tympanicum  partly  covered 
by  the  epithelium  of  the  sulcus  spiralis:  ih,  inner,  ah,  outer  hair-cells,  between  these  the  phalanges  ph, 
forming  the  membrana  reticularis;  ap,  head-plates  of  the  outer,  //,  of  the  inner  pillar-cells.     Techn.  No.  185. 

the  outer  side  of  the  outer  pillars  lie  \.\ie.  outer  hair-cells;  they  resemble  the 
inner  hair-cells,  but  are  characterized  by  a  dark  body  occupying  the  upper 
half  of  the  cell,  the  spiral  body. ^  The  outer  hair-cells  are  arranged  in  several 
( usually  four)  rows ;  they  do  not  lie  in  contact  with  one  another,  but  are  held 
apart  by  Deiters's  cells ;  these  are  elongated  cells  that  contain  a  rigid  fila- 
ment and  possess  at  their  upper  ends  a  cuticular  end-plate  ;  this  has  the  form  of 
a  digital  phalanx.  The  free  spaces  between  the  "  phalanges  "  are  occupied  by 
the  upper  ends  of  the  outer  hair-cells  (Fig.  248).  The  cells  of  Deiters  are 
sustentacuiar  elements  that  exhibit  much  in  common  with  the  pillar-cells;  like 
these  they  consist  of  a  rigid  filament  and  a  protoplasmic  portion  ;  like  these 
they  have  a  head-plate  (named  phalanx).  The  difference  consists  only  in 
this,  that  the  transformation  into  rigid  parts  is  not  so  far  advanced.  The  pha- 
langes are  joined  to  one  another  and  form  a  beautiful  netted  membrane,  the 
membrana  reticularis. 


*  In   the    scheme  (Fig.  247,  A\  this  liody  is  indic.itcd  by  a  (Ltrk  dot  close  licneath  the 
aulitory  hairs. 


266  HISTOLOGY. 

The  outer  hair-cells  do  not  extend  to  the  basilar  membrane,  but  occupy 
only  the  upper  half  of  the  spaces  between  the  cells  of  Deiters ;  the  lower  divi- 
sions of  these  spaces  remain  unoccupied,  and  are  called  NueV s  spaces  (or,  since 
they  communicate  with  one  another,  the  space  of  Nuel),  which  are  inter- 
cellular clefts,  like  the  tunnel,  with  which  they  connect. 

External  to  the  last  row  of  Deiters's  cells  lie  the  cells  of  Heusen,  elongated 
cylinders,  that  gradually  decrease  in  height  and  pass  into  the  indifferent  epithe- 
lium of  the  duct  of  the  cochlea,  whose  elements  over  the  remaining  part  of  the 
basilar  membrane  are  called  the  cells  of  Claudius. 

A  soft,  elastic  cuticular  formation,  the  mem/irana  tectoria,  extends  over  the 
sulcus  spiralis  and  the  organ  of  Corti  (Fig.  249).  It  is  attached  to  the 
vestibular  lip  of  the  sulcus  and  extends  to  the  outermost  row  of  hair-cells. 


The  cochlear  hninch  of  the  auditory  neife  penetrates  into  the  axis  of  the 
cochlea  and  in  its  spiral  uninterrupted  course  gives  off  branches  which  pass  to 
the  root  of  the  osseous  spiral  lamina  ;  here  each  medullated  nerve-fiber  loses  its 
medullated  sheath  and  passes  into  a  nerve-cell  which  like  those  of  the  spinal 
ganglia  possesses  a  connective-tissue  capsule  ;  these  nerve-cells  collectively  form 
the  ganglion  spirale,*  which  winds  along  the  entire  peripheral  spiral  canal  of 
the  cochlea  (Fig.  243).  From  the  opposite  pole  of  each  cell  springs  a  second 
nerve-fiber,  that  soon  acquires  a  medullated  sheath  and  unites  with  neighbor- 
ing fibers  in  a  wide-meshed  plexus  enclosed  within  the  osseous  spiral  lamina  ; 
it  extends  near  to  the  labium  tympanicum,  where  the  fibers  lose  their  medul- 
lated sheath,  escape  through  the  foramina  nervina,  and  end  in  the  epithelium 
in  the  following  manner  :  they  bend  in  the  direction  of  the  turns  of  the 
cochlea  and  run  in  spiral  bundles,  of  which  the  first  passes  to  the  inner  side 
of  the  inner  pillar-cells,  the  second  to  the  tunnel,  the  third  between  the  outer 


*  The  ganglion  spirale  possesses  the  same  structure  as  the  spinal  ganglia,  with   a  single 
difference, — the  ganglion-cells  are  not  unipolar,  but  bipolar,  as  in  the  embryonal  ganglia. 


THE    ORGAN    OF    HEARING.  267 

pillar-cells  and  the  first  row  of  the  cells  of  Deiters,  the  remaining  three  between 
the  cells  of  Deiters.  From  these  bundles  delicate  fibers  proceed  to  the  hair- 
cells,  on  which  (not  within)  they  terminate. 

The  arteries  of  the  labyrinth  come  from  the  auditory  and  the  styloma-stoid 
artery,  which  send  a  branch  through  the  fenestra  rotunda  to  the  cochlea.  The 
auditory  artery  sends  branches  to  the  saccules  and  to  the  semicircular  canals, 
which  in  general  supply  a  wide-meshed  capillary  network,  but  a  close-meshed 
network  on  the  maculse  and  cristfe ;  and  a  branch  to  the  cochlea,  which  on  en- 
tering the  same  breaks  up  into  a  number  of  small  branches.  These  in  part  enter 
the  first  turn,  in  part  ascend  in  the  axis  of  the  cochlea.  From  the  latter 
branches  small  twigs  diverge  successively  and  enter  the  bony  wall  of  the  modio- 
lus, where  they  form  the  radicles  of  smaller  and  larger  masses  of  coiled  blood- 
vessels, the  glomeruli  cochlea  minores  et  majores.  The  smaller  glomeruli  are 
situated  somewhat  above  the  point  of  origin  of  the  osseous  spiral  lamina  and 
supply  capillaries  to  the  limbus  and  to  the  vestibular  membrane.  The  larger 
glomeruli  lie  at  the  root  of  the  septum  between  the  adjoining  turns  of  the 
cochlea  and  supply  two  independent  vascular  territories — the  stria  vascularis 
and  the  lamina  spiralis  membranacea.  The  x'eins  unite  in  the  vas  prominens 
and  in  the  vas  spirale,  which  empty  into  the  vena  spiralis  modioli  lying  beneath 
the  ganglion  spirale  within  the  modiolus.  The  latter  probably  empties  through 
the  aqujeductiis  cochleae  into  the  internal  jugular  vein. 

The  arrangement  of  the  blood-vessels  of  the  cochlea  is  such  that  the  scala 
vestibuli  is  encircled  by  arteries,  the  scala  tympani  by  veins.  The  upper  por- 
tion of  the  scala  tympani  bounding  the  membranous  spiral  lamina  is  thus  com- 
pletely removed  from  the  influence  of  arterial  pulsation. 

The  Lymph-channels. — The  endolymph  in  the  interior  of  the  membranous 
labyrinth  communicates  with  the  subdural  lymph-sijaces  by  means  of  minute 
tubules  passing  from  the  ba,se  of  the  ductus  endolymphaticus.  The  perilym- 
phatic spaces  connect  with  the  subarachnoidal  sjiaces  by  means  of  the  "ductus 
jierilymphaticus."  a  lymph-vessel  running  through  the  aquasductus  cochleiE. 


The  Middle  Ear. 
The  mucous  membrane  of  the  tympanic  cavity  is  intimately  united  with  the 
underlying  periosteum.  It  consists  of  a  thin  connective-tissue  tunica  propria 
and  a  single  stratiun  of  cubical  epithelial  cells,  that  sometimes  on  the  floor, 
occasionally  also  in  larger  areas  of  the  tympanic  cavity,  is  ciliated.  Glands 
(short,  0.1  mm.  long  follicles)  occur  sparingly  in  the  anterior  half  of  the  tym- 
panic cavity.  The  mucosa  of  the  Eustachian  tube  consists  of  a  fibrous  tunica 
propria  (containing  numerous  leucocytes  near  the  pharyngeal  orifice)  and  of  a 
stratified  ciliated  columnar  epithelium  ;  the  ciliary  wave  is  directed  toward  the 
pharynx.  Mucous  glands  occur  in  especial  abundance  in  the  pharyngeal  half 
of  the  tube.  The  cartilage  of  the  Eustachian  tube,  where  it  adjoins  the  bony 
tube,  is  of  the  hyaline  variety,  and  here  and  there  contains  rigid  (not  elastic) 
fibers;  in  the  anterior  portion  the  matrix  is  penetrated  by  dense  networks  of 


268 


HISTOLOGY. 


elastic  fibers.  The  /'lood-vesse/s  in  the  mucosa  of  the  tympanic  cavit)'  form  a 
wide-meshed,  in  the  mucosa  of  the  Eustachian  tube  a  narrow-meshed  super- 
ficial capillary  network,  and  a  deep  capillary  plexus  surrounding  the  glands. 
The  lymph-vessels  run  in  the  periosteum  of  the  tympanic  cavity.  With  regard 
to  the  terminations  of  the  nerves,  exact  information  is  still  wanting. 


Excretorj  duct 


The  External  E.ar. 
The  tympanum  consists  of  a  lamina  of  connective  tissue,  lamina  propria, 
in  which  the  fibrous  bundles  on  the  outer  surface  are  radially  arranged  and 
connected  with  the  periosteum  of  the  sulcus 
tympanicus ;  while  on  the  inner  surface, 
toward  the  tympanic  cavity,  they  are  cir- 
cularly arranged.  On  its  inner  surface  the 
membrane  tympani  is  covered  by  the  mucous 
membrane  of  the  tympanic  cavity,  on  its 
outer  surface  by  the  integument  of  the  exter- 
nal auditory  canal.  Both  investments  are 
very  firmly  attached  to  the  lamina  propria, 
are  smooth,  and  are  without  papillae.  Where 
the  malleus  lies  against  the  tympanum,  the 
latter  is  provided  with  a  superficial  stratum 
of  hyaline  cartilage. 

The  external  auiUfojy  canal,  as  far  as  it 
is  cartilaginous  and  on  the  whole  length  of 
its  upper  wall,  is  clothed  with  an  extension 
of  the  skin  characterized  by  its  thickness  and 
by  a  great  abundance  of  peculiar  coil-glands, 
the    cerinninous  glands.     In  some   respects 
these  glands  correspond  with  the  ordinary 
larger  coil-glands  (sweat-glands)  of  the  skin  ;  like  these,  they  possess  an  ex- 
cretory duct,  lined  by  several  layers  of  epithelial  cells,  and  the  tubules  of  the 
coil  contain  a  simple  layer  of  cubical  gland -cells,  resting  on  smooth  muscle- 


250. —  From  a  Vertical  Section 
B  Skin  of  the  External 
Auditory  Meatus  of  an  Infant.  X  50' 
The  excretory  duct  opens  into  the  hair- 
follicle.     Techn.  No.  189. 


■Section  op  the  Coil-Tubulk  from 

of    a    COIL-TUBULE    FROM  THE    EXTER 

X  240.    Techn.  No.  189. 


Cuticular  border. 

Gland-cells. 
Nuclei  of  smooth  i 
Membrana  propri; 


fibers  and  a  conspicuous  basement  membrane  ;  they  are  distinguished  from  the 
sweat-glands  by  the  very  wide  lumen  of  the  coiled  tubule,  that,  especially  in 
adults,  is  greatly  dilated,  and  by  numerous  pigment-granules  and  fat-droplets 
within   the  gland-cells,  which  frequently  exhibit  a  distinct  cuticular  border. 


THE    NASAL    MUCOUS    MEMBRANE.  269 

The  excretory  ducts  are  narrow,  and  in  children  open  in  the  hair-follicles;  in 
adults,  close  beside  the  hair-follicles  on  the  free  surface.  The  secretion,  the 
cerumen,  consists  of  pigment-granules,  oil-globules,  and  cells  containing  fat ; 
the  latter  probably  come  from  the  sebaceous  glands.  In  the  (remaining) 
region  of  the  bony  external  auditory  meatus,  the  integument  is  thin  and  with- 
out ceruminous  glands. 

The  cartilage  of  the  external  auditory  canal  and  of  the  pinna  is  of  the 
yellow  elastic  variety. 

The  blood-vessels  and  nen'es  are  distributed  as  in  the  skin  elsewhere;  only 
on  the  tympanum  do  they  exhibit  peculiarities.  Along  the  handle  of  the 
malleus  an  artery  descends,  which  breaks  up  into  radially-disposed  branches; 
the  blood  is  returned  by  a  vein  that,  likewise,  runs  along  the  handle  of  the 
malleus.  The  vessels  lie  in  the  integumentary  covering  of  the  tympanum. 
The  mucous  membrane  of  the  tympanum  is  provided  with  a  dense  capillary 
network,  which  anastomoses  with  the  integumentary  vascular  network  by 
means  of  perforating  branches. 

The  lymph-vessels  a.re  ioun^  principally  in  the  cutaneous  stratum  of  the 
tympanum. 

The  nerves  form  delicate  networks  beneath  both  the  mucous  and  the  cuta- 
neous lavers. 


XII.  THE  NASAL  MUCOUS  MEMBRANE. 

The  nasal  mucous  membrane  is  composed  of  three  divisions  differing  in 
structure  :  that  of  the  vestihiilar  region,  that  of  the  respirator}'  region,  and  that 
of  the  olfactory  region. 

THE  VESTIBULAR  REGION. 
The  mucous  membrane  of  the  vestibular  region  (that  lining  the  movable 
nose)  is  a  modified  continuation  of  the  integument  and  consists  of  a  tunica 
propria  beset  with  papillaj  and  covered  by  a  stratified  squamous  epithelium. 
Nuuierous  sebaceous  glands  and  the  hair-follicles  of  the  stiff  nasal  hairs  (vibris- 
sje)  are  embedded  in  the  tunica  propria. 

THE  RESPIR.\TORY  REGION. 
The  respiratory  region  of  the  nasal  mucous  membrane  in  man  includes 
that  lining  all  parts  of  the  nasal  fossre  (and  the  accessory  nasal  spaces),  except 
that  upon  the  median  portion  of  the  superior  turbinal  and  the  corresponding 
part  of  the  nasal  septum.  It  consists  of  a  stratified  ciliated  epithelium,  some- 
times containing  few  goblet-cells,  sometimes  many,  and  of  a  conspicuous 
tunica  propria.  4  mm.  thick  on   the  inferior  turbinal,  which   is  composed  of 


270  HISTOLOGY. 

fibrillar  connective  tissue  and  a  large,  variable  number  of  leucocytes  ;  occasion- 
ally the  latter  form  solitary  nodules.  Migration  of  leucocytes  through  the 
epithelium  into  the  nasal  fossse  also  occurs. 

The  tunica  propria  in  man  contains  branched  tubular  glands,  which  pro- 
duce both  mucous  and  serous  secretion,  and  are  therefore  mixed  glands.  Not 
infrequently  they  open  in  funnel-shaped  depressions,  which  are  lined  by  an 
extension  of  the  superficial  epithelium,  and  on  the  inferior  turbinal  are  per- 
ceptible by  the  unaided  eye. 

In  the  accessory  nasal  spaces  the  epithelium  and  tunica  propria  are  con- 
siderably thinner  ( — o.  02  mm.),  but  otherwise  of  the  same  structure;  the 
glands  are  small  and  few  in  number. 


THE   OLFACTORY  REGION. 

The  olfactory  division  of  the  nasal  mucous  membrane  in  man  is  limited  to 
the  median  portion  of  the  superior  turbinal  and  the  corresponding  part  of  the 


Fig.  252. — Thick  Vertical  Section  of  Respiratory  Mucous  M 

X  20.     The   excretory  ducts  of  two   glands  are  visible.     /.  Funnel-shaped   depl 
No.  191. 

nasal  septum,  and  is  distinguished,  macroscopically,  from  the  rosy  mucosa  of 
the  respiratory  division  by  its  yellowish-brown  color.  It  consists  of  an  epithe- 
lium, the  olfactory  epithelium,  and  of  a  tunica  propria.  In  the  olfactory 
epithelium,  two  forms  of  cells  occur.  The  one  form  is  cylindrical  in  its  upper 
half  and  contains  a  yellowish  pigment  and  minute  granules,  often  arranged 
in  longitudinal  rows.  The  lower  half  is  slenderer,  the  edge  is  serrated  and  in- 
dented, the  inferior  end  is  forked,  and  is  said  to  unite  with  the  similar  ends  of 
neighboring  cells  to  form  a  protoplasmic  network.  These  elements  are  called  si/s- 
tentacular  cells.  Their  nuclei  are  usually  oval  and  lie  at  the  same  level ;  in  ver- 
tical sections  they  are  seen  to  occupy  a  narrow  belt,  the  zoiie  of  the  oval  nuclei 
(Fig.  255).  The  second  form  of  cells  possesses  a  spherical  nucleus  and  only  in 
the  vicinity  of  the  latter  an  appreciable  amount  of  protoplasm ;  from  this  a 
slender  ciliated  cylinder,  the  attenuated  cell-body,  extends  upward,  while  from 
the  opposite  pole  a  very  delicate  process  continues  directly  into  the  axis-cylin- 
der of  a  nerve-fiber.  These  cells,  the  olfactory  cells,  are  ganglion-cells,  and 
their  louer  i)rocess  a  centripetal  nerve-fiber.     Their  round  nucleolated  nuclei 


THE    NASAL   MLXOUS    MEMBRANE. 


271 


lie  at  different  levels  and  occupy  a  broad  belt,  the  zone  of  the  round  nuclei. 
Occasionally,  in  the  nonnucleated  ei)ithelial  territory,  round  nuclei  in  varying 
number  are  found  above  the  zone  of  the  oval  nuclei  ;  they  belong  to  dislocated 
olfactory  cells,  or  are  the  nuclei  of  wandering,  often  pigmented,  leucocytes.  In 
addition  to  these  two  kinds  of  cells,  there 
are  intermediate  forms,  which  sometimes 
resemble  the  olfactory  elements,  some- 
times the  sustentacular  cells.  At  the  border 
of  the  epithelium,  toward  the  connective 
tissue,  is  a  protoplasmic  network  furnished 
with  nuclei,  the  so-called  basal  cells  (Fig. 
256,  ^).  The  surface  of  the  epithelium  is 
covered  by  an  extremely  delicate  homo- 
geneous membrane,  the  membrana  litnitans 
olfactoria ;  it  is  pierced  by  the  ciliated  ex- 
tremities of  the  olfactory  cells  and  is  covered 
by  a  peculiar  substance,  regarded  by  some 
authors  as  a  cuticular  formation  similar  to 
the  basal  border  of  the  intestinal  epithelium, 

by  others  as  delicate  cilia,  by  still  others  interpreted  as  minute  jiarticles  of 
discharged  mucus  (Fig.  253,  s). 

The  tunica  propria  consists  of  a  loose  feltwork  of  rigid  connective-tissue 
fibers  intermingled  with  delicate  elastic  fibers,  which  in  some  animals  toward 
the  epithelium  (for  example,  in  the  cat)  is  condensed  to  a  structureless  mem- 
brane.     Numerous  glands,  the  so-called  olfactory  (^Bowman' s)  glands,  are  em- 


53, — Isolated  Cblls  of  the  Olpac- 
^  Mucosa  of  Rabbit.    X  560.   st.  Sus- 


tenucttU 

bling  (         .     . 

process  has  been  torn  oflf;y".  1 

^,  cells  of  olfactorj' glands. 


.  olfactory'  < 


r'  the  lower 
ilialcd  cells  ; 
:hn.  No.  190. 


Bundles  of  fibers  of  olfactory  nerve. 
KiG.  354. — Vrrtical  Section  thkough  the  Olfactory  Re 


ripetal  process  of  an  olfactorj'  cell. 

3F  A  Vouxc  Rat.    X  480.     lechn.  No.  193. 


bedded  in  the  tunica  propria;  they  are  either  sim|)le  or  (for  example,  in  man) 
branched  tubules,  in  which  an  excretory  duct,  situated  in  the  epithelium,  a 
body  and  a  fundus  may  be  distinguished.  The  cells  of  the  body  of  the  glands 
are  pigmented.  The  glands  were  until  recently  regarded  as  serous  glands,  but 
latterly  they  have  been  pronounced  mucous  glands.      The  olfactory  glands  fre- 


272 


HISTOLOGY. 


quently  advance  beyond  the  territory  of  the  olfactory  mucous  membrane,  and 
are  found  in  the  adjoining  portions  of  the  respiratory  mucous  membrane. 
The  tunica  propria  also  carries  the  ramifications  of  the  nerves.  The  branches 
of  the  olfactory  nerve   are  accompanied  by  processes  of  the  dura  and  consist 


■«?;,,#     )  Tunica  propri 


Fig.  255. — Vertical  Section  of  Olfactorv  Mucosa  of  Kahbit.  X  50.  zo.  Zone  of  oval  nuclei ;  zr,  zont 
round  nuclei  ;  dr,  olfactory  glands  ;  a,  excretory  duct ;  k,  body  ;  ^,  fundus ;  n,  branches  of  olfactory  ne 
cut  transversely  ;  z*,  veins  ;  ar,  arteries  ;  6,  bundles  of  connective  tissue  in  cross-section.     Techn.  No.  19 


throughout  of  nonmeduUated  fibers,  that  readily  separate  into  their  component 
fibrillse ;  the  fibers  are  the  inferior  processes  of  the  olfactory  cells,  grouped 
in  bundles,  which  pass  in  horizontal  arches  from  the  epithelium,  descend  into 


%>-•'■ 


Fig.  256. — Vertical  Section  through  the  Olfactory  Mucosa  of  Rabbit.  X  560.  s.  Cuticular  border 
zo,  zone  of  oval  nuclei ;  zr,  zone  of  round  nuclei .  i,  b.-is.il  cells  ;  dr,  portions  of  olfactory  glands,  on  ihc 
right  the  lower  portion  of  the  excretory  duct  is  visible  ;  «,  branch  of  the  olfactory  nerve.      Techn.  No   192 


the  tunica  propria,  and  by  union  with  neighboring  bundles  form  the  branches  of 
the  olfactory  nerve.  The  terminal  ramifications  of  the  trifacial  nerve  lie  within 
the  tunica  propria ;  delicate  fibers  that  ascend  to  the  epithelium  and  there  ter- 
minate in  free  ends  possibly  belong  to  the  trifacial  nerve. 


THE    TASTE-BUDS.  273 

Of  the  l>/o(hi-vi-ssels  of  the  nasal  mucosa  the  stems  of  the  arteries  run  in 
the  deeper  strata  of  the  tunica  propria  ;  they  break  up  into  a  rich  subepithelial 
capillary  network.  The  veins  are  remarkable  for  their  size,  and  over  the  poste- 
rior end  of  the  inferior  turbinal  form  so  dense  a  network  as  to  give  the  tunica 
propria  the  character  of  cavernous  tissue  (Fig.  252  and  Fig.  255). 

The  lymph-vessels  form  a  coarse-meshed  net  lying  in  the  deeper  strata  of 
the  tunica  propria.  The  lymph-vessels  of  the  olfactory  mucosa  may  be  injected 
from  the  subarachnoidal  space,  through  the  perineuria!  sheaths  of  the  branches 
of  the  olfactory  nerve,  acquired  from  the  cerebral  membranes  on  passing  through 
the  cribriform  plate. 

Medullated  twigs  of  the  trifacial  nerve  may  be  found  in  the  respiratory 
as  well  as  in  the  olfactorv  mucosa. 


XIII.  THE  TASTE-BUDS. 

The  tastc-hiids  or  gustatory  organs  are  oval  bodies,  about  80  /x  long  and 
40  //  broad,  which  are  completely  embedded  in  the  epithelium  of  the  oral  mucous 
membrane  ;  their  base  rests  upon  the  tunica  propria,  the  upper  end  reaches  to 
the  surface  of  the  epithelium,  which  at  this  point  exhibits  a  funnel-shaped  de- 


KlG.  257.— Vkktical  Section  of  Two  Rinr.Rs  ,,r  1'aiilla  Foliata  of  Rabbit.  X  80.  Ea.:h  ridge. 
/,  bears  secondary  ridges,  /';  ^,  taste-buds;  «,  medullated  nerves;  d,  serous  gland;  a,  portion  of  an  ex- 
cretory duct  of  a  serous  gland  ;  m,  muscle-fibers  of  tongue.     Tcchn.  No.  195. 

pression,  the  taste-pore.  Each  taste-bud  consists  of  two  kinds  of  elongated  epithe- 
lial cells  ;  the  one  are  either  of  the  same  diameter  throughout,  or  they  taper  at 
the  basal  end,  which  occasionally  is  forked,  while  the  upper  end  is  prolonged  to 
a  fine  pointed  e.\tremity  ;  their  protoplasm  is  clear.  These  cells  constitute  the 
bulk  of  the  ta.ste-bud,  are  princi|)ally  situated  at  the  periphery,  and  are  called 


2  74  HISTOLOGY. 

tegmental  cells.  They  serve  as  support  and  sheath  for  the  gustatory  cells, 
which  are  the  real  percipient  epithelial  elements.  The  gustatory  cells  are  small, 
and  only  slightly  enlarged  where  the  nucleus  is  situated  ;  the  latter  is  sometimes 
near  the  lower  or  central  end,  sometimes  in  the  middle,  rarely  at  the  upper 
or  peripheral  end  of  the  cell.  The  upper  division  of  the  cell  is  cylindrical,  or 
more  frequently  conical,  and  bears  on  its  free  end  a  stiff,  refractile,  hair-like 
process,  a  cuticular  formation  (Fig.  258)  ;  the  lower  division  is  sometimes 
slender,  sometimes  thick  and  blunted  at  the  end  or  expanded  into  a  triangular 


Tunica  propria. 
Fig.  258.— From  a  Vertical  Section  of  Papilla  Foliata  of  Rabbit.     X  560.    Techn.  No.  195. 

foot,  which  does  not  however  extend  into  the  fibrous  tissue  of  the  mucosa. 
Their  protoplastn  is  granular.  Not  infrequently  many  leucocytes  are  found  in 
the  interior  of  the  taste-bud. 

The  taste-buds  occur  chiefly  in  the  lateral  walls  of  the  circumvallate  pa- 
pillae and  on  the  ridges  of  the  papillae  foliatse,  also  occasionally  on  the  papillae 
fungiformes,  on  the  soft  palate,  and  on  the  posterior  surface  of  the  epiglottis. 

Taste-pore.  ~1 

I 

\  Taste-bud. 

',   X'Sv"^'       .    I  \^ " Gustatory  cells. 

Epithel 


Inlergemmal  nerve-fibers.         Intragemmal  nerve-fibers. 

Fig.  259. — From  a  Vertical  Section  of  a  Circumvallate  P.apilla  of  Monkey.     X  240. 
Techn.   No.  196. 

The  conjecture  that  the  terminal  ramifications  of  the  glossopharyngeal 
nerve  have  the  same  anatomical  relation  to  the  gustatory  cells  that  the  olfactory 
nerve-fibers  have  to  the  olfactory  cells  has  been  shown  to  be  erroneous.  The 
terminal  branches  of  the  glossopharyngeal  nerve  consist  of  medullated  and 
gray  nerve-fibers  beset  with  microscopic  (sympathetic)  ganglia,*  which  form  a 
dense  plexus  in   the  tunica  propria,  from  which   numerous  branches  spring. 

*  Whether  the  so-called  "taste-granules  "  beneath  the  epithelium  of  the  papillse  foliatse  are 
multipolar  nerve-cells  is  very  questionable ;  a  nerve-process  has  not  as  yet  been  demonstrated. 


THE    TASTE-BUDS.  275 

Some  of  the  latter  terminate,  possibly,  in  the  connective  tissue  in  end-bulbs,  but 
the  majority  of  the  gray  fibers  penetrate  into  the  epithelium.  Here  two  kinds 
of  fibers  may  be  distinguished.  The  one  kind,  the  "  intragemmal  "  fibers, 
enter  the  taste-buds,  divide,  and  form  a  plexus  beset  with  numerous  conspicuous 
varicosities  that  extends  up  to  the  taste-pore ;  these  fibers  do  not  anastomose 
with  one  another,  nor  do  they  connect  with  the  gustatory  cells,  but  all  terminate 
in  free  ends.  The  other,  the  smoother  "  intergemmal "  fibers,  penetrate  the 
epithelial  areas  between  the  taste-buds  and,  usually  without  dividing,  extend 
to  the  uppermost  strata  of  the  epithelium. 


PART   111. 

SPECIAL  TECHNIQUE. 


Protopla 


Nucleus.  );—:. 


t    Nuclear  membrai 

2  Chromatin  cords. 

3  Nucleoli. 


I.   KARYOKINESIS. 

Xo.  I. — For  the  study  of  nuclear  structure  and  karyokinesis  amphibian 
larvK  are  most  suitable.  Those  most  readily  procured  are  the  larvae  of  the 
water  salamander,  which  in  the  months  of  June  and  July  abound  in  every  pool. 
Place  freshly-caught  specimens,  3  to  4  cm.  long,  in  about  100  c.c.  of  chromo- 
acetic  acid  (p.  21).  After  3  hours  place  the  larvae  in  running  water  for 
8  hours,  and  then  in  70  per  cent,  alcohol.  At  the  expiration  of  4  hours,  or 
later,  the  objects  are  ready  for  further  treatment. 

a.  Nuclear  Stnicttirc. — With  a  scalpel  carefully  scrape  the  epithelium 
from  the  skin  of  the  abdomen,  with  two  pairs  of  delicate  forceps  strip  off  the 

thin   corium,  stain   it    i   to   3  minutes  in 
,  5    c.c.  of  Bohmer's  hematoxylin  (p.  31), 

and  mount  in  damar-varnish  (p.  38). 
Between  the  round  glands  beautiful  con- 
nective-tissue cells  with  large  nuclei  may 
be  seen.  The  structure  of  the  protoplasm, 
the  centrosome  and  attraction-sphere,  also 
the  structure  of  the  nucleus  can  only  be 
recognized  by  the  employment  of  com- 
plicated methods  and  high  magnification. 
The  results  obtained  by  ordinary  methods 
are  like  that  pictured  in  Fig.  260. 

The  cross-striped  muscles  of  the  tail 
and  the  membranes  of  smooth  muscle-fiber 
( the  latter  may  be  readily  obtained  by 
stripping  off  the  muscularis  of  the  intes- 
tine) also  furnish  instructive  slides. 

b.  Kaiyokinesis. — With  a  pair  of  fine  scissors  cut  round  the  margin  of  the 
cornea,  and  strip  off  the  same  ;  stain  and  preserve  like  a.  The  preparation  must 
be  placed  on  the  slide  with  the  convex  surface  of  the  cornea  upward  ;  in  the 
epithelium,  even  with  the  low-power  objective,  many  karyomitotic  figures  may 
be  seen,  which  may  be  recognized  by  their  intense  color.  By  this  method  the 
nuclear  spindle  and  polar  radiation,  as  in  Fig.  5,  can  only  be  perceived  (with 
higher  magnification)  in  especially  favorable  preparations,  e.  g.,  eggs  of  siredon 
and  the  trout. 

The  delicate  lamellae  suspended  from  the  convex  side  of  the  cartilaginous- 
gill-arch,  as  well  as  the  epithelium  of  the  floor  of  the  oral  cavity,  are  very 
suitable  objects.  Occasionally  not  a  single  karyokinetic  figure  is  found.  Isolated 
figures  may  sometimes  be  observed  in  preparation  a. 

276 


Fig.  260. — Connective-tissue  Cell  from 
Corium  of  Triton  T-^niatus.  Surface 
View.  X  560.  Only  the  coarser  filaments 
of  the  nuclear  network  can  be  distinctly  seen  : 
with  this  magnification  the  finer  filaments  ap- 
pear as  minnie  dots,  the  niicleoH  as  parts  of  the 
nuclear  network. 


SPECIAL   TECHNIQUE.  277 


II.   CILIATED  El'ITHEI.IAL  CELLS. 

No.  2. — To  obtain  living  ciliated  cells,  kill  a  frog  (p.  25),  place  it  on 
its  back  and  with  scissors  cut  off  the  lower  jaw,  so  that  the  roof  of  the  cavity 
of  the  mouth  is  exposed.  From  the  mucosa  of  the  roof  cut  out  a  small  strip 
about  5  mm.  long,  place  it  on  the  slide  in  adroj;  of  salt  solution,  and  apply  a 
cover-gla.ss.  Examine  with  the  high  power  and  search  the  edges  of  the  pre- 
paration. At  first  the  movement  of  the  cilia  is  very  lively,  so  that  the  observer 
cannot  see  the  individual  cilia  ;  the  entire  ciliated  border  waves  ;  the  motion 
ha.s  been  compared  to  a  cornfield  swayed  by  the  wind.  After  a  few  moments 
the  rapidity  of  the  movement  diminishes  and  the  cilia  can  be  plainly  seen.  If 
the  movement  ceases,  it  can  be  restored  by  the  application  of  a  drop  of 
concentrated  potash  solution  (p.  41);  the  effect  is  transient,  so  that  the  eye 
of  the  observer  must  not  be  removed  from  the  ocular  while  the  fluid  passes 
under  the  cover-glass.     The  addition  of  water  soon  suspends  the  movement. 

III.   CONNECTIVE  TISSUE. 

No.  3. — Mucous  Connective  Tissue. — Place  the  umbilical  cord  of  a  3  to  4 
months'  human  embryo  (or  pig  embryo  3  to  6  cm.  long)  in  100  c.c.  of  Miiller's 
fluid  (p.  20)  3  to  4  weeks;  harden  in  30  c.c.  of  gradually  strengthened 
alcohols  (p.  29).  The  cord  will  still  be  very  soft;  in  order  to  obtain  good 
sections  it  must  be  embedded  in  liver,  and  in  cutting  must  be  somewhat  com- 
pressed with  the  fingers.  The  section  may  be  stained  in  picrocarmine  (12  hours) 
or  in  hemato.xylin  (  5  minutes  j,  and  should  be  examined  in  a  drop  of  distilled 
water.  In  glyceflne  and  damar-varnish  the  delicate  proces.ses  of  the  cells  and 
the  bundles  of  connective  tissue  are  invisible.  In  the  vicinity  of  the  blood- 
ves.sels  the  network  of  cells  is  less  fine ;  therefore  a  field  remote  from  the 
blood-vessels  should  be  selected  for  study.  The  older  the  embryo,  the  greater 
is  tiie  number  of  the  connective-tissue  bundles.  Mount  in  diluted  glycerine 
(p.  21). 

No.  4. — Fibrous  Connective  Tissue  ;  Connective-tissue  Bundles. — Prcjiare 
small  strii)s,  i  to  2  cm.  long,  of  intermuscular  connective  tissue,  for  examjile, 
of  the  thin  septum  between  the  serratus  and  intercostal  muscles ;  place  a  small 
piece  on  a  dry  slide  and  quickly  spread  it  out  with  teasing  needles  (see  "  half- 
drying  method,"  No.  27  a,  p.  281  ),  add  a  drop  of  salt  solution  and  apply  a 
cover-glass.  The  bundles  of  connective  tissue  appear  wavy  and  pale;  with  a 
little  jjractice  the  sharply-contoured,  highly-refracting  elastic  fibers  may  be  dis- 
tinguished, and  also,  in  favorable  situations,  the  nuclei  of  the  connective-tissue 
cells. 

No.  5. — The  cells  of  fibrous  connective  tissue  may  be  rendered  visible  by 
the  addition  of  a  drop  of  picrocarmine  to  preparation  No.  4,  under  the  cover- 
glass  (p.  41).  In  most  cases  only  the  red  nucleus  can  be  perceived,  especially 
when  the  cell  lies  wholly  upon  the  fibrous  bundles.  In  rare  cases  the  jiale 
yellow,  variously-shaped  body  of  the  cell  can  be  seen  (Fig.  22,  A,  i,  2,  3). 

No.  6. — Afastzellen  (granule-cells). — Fix  small  pieces,  i  to  2  cm.  square, 
of  mucous  membrane  (of  the  mouth,  of  the  pharynx,  or  of  the  intestine)  in 
absolute  alcohol  (  p.  27).  In  from  3  to  8  days  cut  thin  sections  and  stain  them 
in  10  c.c.  of  alum-carmine  dahlia  for  24  hours  (p.  23).  Transfer  them  to  10  c.c. 
of  ab.solute  alcohol  for  24  hours,  which  must  be  renewed  once  or  twice  during 
this  time.  Mount  in  damar  (p.  38).  The  protoplasm  of  the  Mastzellen  then 
exhibits  granules  stained  an  intense  blue. 


2  76  HISTOLOGY. 

No.  7. — Fibril/a. — Place  a  piece  of  tendon  about  2  cm.  long  in  a  saturated 
aqueous  solution  of  picric  acid.  On  the  following  day,  with  two  pairs  of  forceps, 
\m\\  the  tendon  apart  along  its  length,  take  from  the  interior  a  bundle  about  5 
mm.  long,  and  tease  the  same  on  a  dry  slide  {cf.  No.  27  a,  p.  281),  add  a  drop 
of  distilled  water,  apply  a  cover-glass,  and  examine  with  the  high-power  objec- 
tive.    The  ultimate  fibrillce  appear  as  exceedingly  fine,  silky  filaments. 

No.  8. — "Enci/r/ing  Fibers." — With  the  scissors  cut  out  a  piece  about  i 
cm.  square  of  the  connective  tissue  within  the  arterial  circle  of  Willis,  wash  it 
in  a  watch-glass  in  salt  solution,  with  needles  spread  it  out  in  a  drop  of  the  same 
solution  on  a  slide,  and  cover.  With  the  low  power,  in  addition  to  numerous 
delicate  blood-vessels  and  ordinary  bundles  of  fibrous  tissue,  sharply-contoured, 
refracting  bundles,  in  distinct  contrast  to  the  remaining  connective  tissue, 
will  be  found,  which,  on  the  use  of  the  high  power  and  a  diaphragm  of 
narrow  aperture,  show  that  they,  likewise,  consist  of  fibrillar  connective  tissue. 
Place  such  a  bundle  in  the  field  and  treat  it  with  a  drop  of  acetic  acid  under 
the  cover-glass  (p.  41).  As  soon  as  the  acid  reaches  the  bundle,  it  swells, 
the  fibrillation  vanishes,  and  instead  elongated  nuclei  appear.  The  swell- 
ing is  not  uniform  ;  at  irregular  intervals  the  bundle  is  constricted.  With  dim 
illumination  the  "fibers"  (cell  remnants)  producing  the  constrictions  mav 
be  seen  (Fig.  22,  B). 

No.  9. — Fat-cells. — Take  a  small  piece  of  the  reddish-yellow,  gelatinous 
fat  from  the  axilla  of  an  emaciated  individual ;  spread  out  rapidly  a  piece  the 
size  of  a  split  pea  in  the  thinnest  possible  layer  on  a  dry  slide,  add  imtneJiately 
a  drop  of  salt  solution,  and  apply  a  cover-glass.  In  thin  places  atrophic  fat- 
cells,  like  those  shown  in  Fig.  23  B,  will  be  seen.  This  pjeparation  may  be 
stained  under  the  cover-glass  with  picrocarmine  (p.  41)  and  preserved  in 
diluted  glycerine.  Ordinary  (normal)  fat-cells,  taken  from  any  part  of  the 
body,  are  likewise  to  be  examined  in  salt  solution.  The  spherical  cells  should 
be  studied  with  change  of  focus  {^cf.  Fig.  23,  A^. 

No.  10. — Fine  elastic  fibers  may  be  readily  obtained  by  treating  prepara- 
tion No.  4,  under  the  cover-glass,  with  a  few  drops  of  acetic  acid.  The  con- 
nective-tissue bundles  swell  and  become  transparent,  the  elastic  fibers,  on  the 
contrary,  remain  unaltered,  and  stand  out  sharply  contoured  (Fig.  20,  A'). 

No.  II.  —  Thicker  elastic  fibers  may  be  obtained  by  teasing  in  a  drop  of  salt 
solution  a  slender  piece,  about  5  mm.  long,  of  the  fresh  ligamentum  nuchre  of 
an  ox  (Fig.  20,  j9).  The  piece  should  not  be  taken  from  the  loose,  envelop- 
ing tissue,  but  from  the  tough,  yellowish  fibrous  portion.  The  preparation 
may  be  stained  in  picrocarmine  and  mounted  in  glycerine. 

No.  12.  —  Cross-sections  of  thick  elastic  fibers  may  be  obtained  by  drying  a 
piece  (10  cm.  long  and  i  to  2  cm.  thick)  of  the  ligamentum  nuchse  (it  will  be 
ready  to  use  in  4  to  6  days)  and  treating  it  like  No.  63. 

No.  13. — Fenestrated  Membranes. — Take  a  small  piece  (about  5  mm. 
square)  of  endocardium,  place  it  in  a  drop  of  water  on  a  slide,  and  add, 
under  the  cover-glass,  i  to  2  drops  of  potash-lye.  Examine  the  edges  of  the 
preparation  (Fig.  21). 

Good  specimens  may  also  be  obtained  from  the  basilar  artery  ;  place  a 
]nece  of  the  artery  cut  open  lengthwise  in  10  c.c.  of  concentrated  potash  solu- 
tion. After  6  hours  take  a  small  piece,  about  i  cm.  long,  and  separate  the 
lamellae  in  a  drop  of  water  on  a  slide  ;  this  is  easily  done  by  scraping  it  with  a 
scalpel.  Cover  and  examine  with  the  high  power.  The  small  apertures  in  the 
membrane  have  the  appearance  of  shining  nuclei. 


SPECIAL    TECHNIQUE.  279 

With  the  low  power  the  membrane  is  to  be  recognized  by  its  dark  outlines. 
To  preserve,  wash  it  well  in  lo  c.c.  of  water  (5  minutes),  stain  it  in  3  c.c.  of 
Congo  red  from  12  to  20  hours  (p.  23),  and  mount  in  damar. 

No.  14.  — Hyaline  Cartilage. — Cut  off  the  extremely  thin  episternum  of  the 
frog,  place  it  on  a  dry  slide,  cover  it  with  a  cover-glass,  and  examine  at  once 
with  the  high  power.  The  cartilage-cells  completely  fill  the  lacunre  (Fig. 
25,  A).      For  prolonged  study,  add  a  drop  of  saline  solution. 

No.  15. — Hyaline  Costal  Cartilage. — Without  any  previous  preparation  fine 
sections  of  costal  cartilage  may  be  cut  with  a  dry  razor,  and  examined  in  a  drop 
of  water.  Search  for  one  of  the  glossy  areas  containing  rigid  fibers  (Fig.  25,  .5). 
The  preparation  may  be  preserved  by  adding  a  few  drops  of  dilute  glycerine. 

Fresh  cartilage  does  not  stain  readily.  The  tissue  must  first  be  placed  in 
Kleinenberg's  picrosulphuric-acid  mixture  or  in  Miiller's  fluid  and  then  in 
alcohol  (p.  29)  and  subsequently  stained  with  Bohmer's  hematoxylin  (p.  22). 
Mounted  in  damar,  which  clears  vigorously,  the  finer  details  vanish. 

No.  16. — Elastic  Cartilage. — Take  a  piece  of  the  arytenoid  cartilage  of  man 
(better  still  of  the  ox) — the  elastic  cartilage  of  the  anterior  angle  is  recognized 
by  its  yellowish  color.  Cut  a  section  that  includes  the  boundary  line  between  the 
elastic  and  hyaline  cartilage,  and  examine  it  in  water.  Preserve  like  No.  15. 
The  development  of  the  elastic  fibers  may  often  be  studied  in  the  cartilages  of 
adults,  especially  in  the  epiglottis  and  in  tlie  vocal  process  of  the  arytenoid 
cartilage  (Fig.  26,  i). 

No.  17. —  ]V}iite  Fibro-cartilage. — Cut  the  intervertebral  disks  of  adult  man 
in  pieces  from  i  to  2  cm.  square  ;  fix  in  100  c.c.  of  picrosulphuric  acid  (p.  20). 
for  24  hours  and  harden  in  50  c.c.  of  gradually  strengthened  alcohols  (p.  29). 
Stain  sections  in  Bohmer's  hematoxylin  (p.  22)  and  mount  in  damar  (p.  38). 
Sections  through  the  edges  yield  hyaline  cartilage  ;  sections  through  the  central 
portions  of  the  disk  exhibit  large  groups  of  cartilage-cells. 

IV.   MUSCLE-FIBERS. 

No.  1 8. — Striated  Mtisclc-filiers. — a  {of  the  frog') . — With  the  scissors  placed 
flat  and  parallel  to  the  course  of  the  fibers,  cut  a  piece  about  i  cm.  long  from 
the  adductor  muscle  of  a  recently-killed  frog.  Take  a  fragment  from  the 
inner  surface  of  this  piece  and  tease  it  in  a  small  droj)  of  salt  solution,  add  a 
second  larger  drop  of  the  same  liquid  and,  without />ressing,  cover  the  prepara- 
tion with  a  cover-glass.  With  low  magnification  (50  diameters)  the  cylindrical 
form,  the  difference  in  thickness,  occasionally  also  the  cross-striation  of  the 
isolated  fibers  may  be  seen  (Fig.  34).  With  higher  magnification  (240 
diameters)  the  cross-striation  is  distinctly  visible,  and  occasionally  pale  nuclei 
and  refracting  granules.  The  presence  of  numerous  granules  within  the  muscle- 
fibers  is  probably  an  indication  of  active  metabolic  processes.  Where  the 
muscle-fibers  are  cut  acro.ss,  the  muscle-substance  not  infrequently  protrudes 
from  the  sarcolemma. 

/'  {of  man). — I  have  found  beautiful  striated  fibers  in  muscles  taken  from 
the  human  cadaver  injected  with  carbolic  acid. 

To  i)reserve,  stain  under  the  cover-glass  with  picrocarmine  (p.  41)  for 
about  5  minutes,  and  then  displace  the  staining  fluid  with  diluted  glycerine. 

No.  19.  —  The  Sarcolemma. — Treat  preparation  No.  18  a  with  a  couple  of 
drops  of  ordinary  water.  In  2  to  5  minutes  it  will  be  seen,  with  the  low  power 
(  tO  diameters^,  that  the  sarcolemma  is  raised  from  the  muscle-substance  in  the 


2  So  HISTOLOGY. 

form  of  transparent  blebs,  and  at  other  places,  where  the  torn  muscle-substance 
has  retracted,  the  sheath  appears  as  a  delicate  line  spanning  the  interval 
(Fig.  34,  I,  s,  s'). 

No.  20. — Muscle  Nuclei. — Prepare  muscle-fibers  like  Xo.  iS  a.  Treat 
with  a  drop  of  acetic  acid  (p.  41).  The  shrunken  but  sharply-outlined  nuclei, 
with  the  lower  power,  have  the  appearance  of  spindle-shaped  streaks 
(Fig.  34,  2). 

No.  21. — Fibrilla. — Place  the  fresh  muscle  of  a  frog  in  20  c.c.  of  o.  i 
per  cent,  chronaic-acid  solution  (p.  20).  In  about  24  hours  the  tissue  may  be 
teased  in  a  drop  of  water,  and  fibers  will  be  found  whose  ends  have  separated 
into  their  ultimate  fibrillffi  (Fig.  34,  2  ).  If  it  is  desired  to  make  a  permanent 
preparation,  place  the  muscle  in  water  for  i  hour,  then  in  20  c.c.  33  per 
cent,  alcohol,  10  to  20  hours  ;  tease  at  once  or  preserve  in  70  per  cent, 
alcohol  until  wanted,  and  then  isolate  (p.  25).  If  the  chromic  acid  be 
removed  by  allowing  the  tissue  to  remain  in  alcohol  (frequently  renewed)  for 
several  weeks,  the  teased  preparation  may  then  be  stained  with  picrocarmine 
in  the  moist  chamber  and  this  replaced  by  glycerine  (p.  41). 

No.  22. — The  Ends  of  the  Muscle-Ji/>e?-s. — Place  the  fresh  gastrocnemius 
muscle  of  the  frog  in  20  c.c.  of  concentrated  potash-lye,  and  cover  the  watch- 
glass.  In  about  30  to  60  minutes  (in  a  cold  room,  somewhat  later)  the 
muscle,  if  lightly  moved  with  a  glass  rod,  falls  into  its  fibers.  Should  this 
fail,  the  solution  is  not  strong  enough  (see  p.  26).  Transfer  a  number  of  the 
fibers  in  a  drop  of  the  same  solution  to  a  slide  and  carefully  apply  a  cover- 
glass.  With  the  low  power  the  ends  of  the  muscle-fibers  and  numerous  nuclei 
may  be  seen  (Fig.  34,  3).  The  fibers  should  not  be  examined  in  water  or 
glycerine,  since  the  lye,  thus  diluted,  soon  destroys  them. 

No.  23. — Branched  Muscle-fibers. — Remove  the  tongue  from  a  recently- 
killed  frog  (it  is  attached  in  front  to  the  lower  jaw,  is  free  behind)  and  place 
it  in  20  c.c.  of  pure  nitric  acid,  to  which  about  5  gm.  of  ])otassium  chlorate 
have  been  added  (some  undissolved  chlorate  must  remain  in  the  bottom 
of  the  vessel).  In  a  few  hours,  with  glass  rods  carefully  transfer  the  tongue 
to  30  c.c.  of  distilled  water,  which  must  be  frequently  changed.  In  this  the 
tissue  can  remain  a  week,  though  it  may  be  used  at  the  end  of  24  hours.  For 
this  purpose  put  it  in  a  test-tube  half  filled  with  water  and  shake  it  several 
minutes  ;  the  tongue  will  fall  to  pieces.  Turn  the  contents  of  tlie  test-tube  into 
a  capsule,  and  in  an  hour  or  later  place -a  little  of  the  sediment  that  has  been 
deposited  in  the  meanwhile  in  a  drop  of  water  on  a  slide.  The  tissue  may  be 
further  isolated  with  the  teasing  needles,  but  in  most  cases  this  is  superfluous. 
Examine  with  the  low  power.  Stain  under  the  cover-glass  with  picrocarmine 
(p.  41).     Mount  in  dilute  glycerine  (p.  21).      (Fig.  34,  4.) 

No.  24. — Smooth  Musclefibers. — These  are  best  isolated  by  placing  a 
piece  of  the  stomach  or  intestine  of  a  frog,  just  killed,  in  20  c.c.  of  potash 
solution  and  treating  like  No.  22  (Fig.  31). 


V.   NERVE-CELLS  AND  NERVE-FIBERS. 

No.  25.  —  Ganglion-cells,  Fresh. — Tease  a  small  piece  of  the  Gasserian 
ganglion  in  a  drop  of  salt  solution,  and  stain  under  the  cover-glass  with  picro- 
carmine for  2  minutes  (p.   41).     The  processes  of  the  cells  usually  tear  off. 

The  ganglion-cells  of  the  cerebral  and  cerebellar  cortex  may  be  prepared 
in  the  same  way  ;   the  processes  likewise  are  easily  lost. 


SPECIAL   TECHNIQUE. 


281 


i  cylinde 


Medullary  sheath. 


No.  26. — Multif>olar  Ganglion  of  the  Spinal  Cord. — Remove  with  the 
scissors  as  much  as  jjossible  of  the  white  substance  of  the  spinal  cord  of  an  ox. 
and  i)tace  the  gray  remnant  in  pieces  i  to  2  cm.  in  length  in  30  c.c.  of  33  jJer 
cent,  alcohol  (p.  19,  3,  </).  In  36  to  48  hours  transfer  the  pieces  to  20  c.c.  of 
undiluted  neutral  carmine  solution  (p.  23 )  for  24  hours.  The  now  very  soft 
pieces  should  be  transferred  with  the  section-lifter  to  50  c.c.  of  distilled  water, 
in  order  to  wash  out  some  of  the  stain,  and  after  10  minutes  spread  with 
needles  in  a  thin  layer  on  a  dry  slide.  The  ganglion-cells  can  be  distinguished 
by  their  bright  red  nuclei  ;  the  cell-body  and  the  ])rocesses  are  not  visible. 
Let  the  preparation  dry  thoroughly  and  mount  in  damar  (Fig.  38). 

No.  2-].— Fresh  .\fedullated  Nen<e-fil>ers. — Expose  the  sciatic  nerve  of  a 
frog  just  killed,  and  with  delicate  scissors  cut  it  at  the  level  of  the  popliteal 
space  and  about  i  cm.  higher.      Isolate  in  a  drop  of  salt  solution. 

No.  27  a. — Better  still,  tease  on  a  dry  slide  by  the  "half-drying" 
method.  Hold  the  linocr  end  of  the  nerve  with  one  needle,  with  another 
needle  separate  the  nerve-bundles  along  half  the  length  of  the  nerve;  a  thin 
shining  membrane  will  span  the  interval  between  the  sejiarated  bundles.  Add 
a  drop  of  salt  solution  and  apply  a  cover-glass.  The  membrane  contains  numer- 
ous isolated  nerve-fibers.  The  mani- 
pulation must  be  done  very  rapidly  (in 
a1)ont  15  seconds),  so  that  the  nerve- 
fibers  do  not  become  dry  (  Fig.  41,  6, 
7,  8,  9)- 

No.  28. — Alterations  in  the  Med- 
ullary Sheath. — Treat  No.  27  a  with 
water  ( place  a  drop  at  the  edge  of  the 
cover-glass  and  let  it  flow  under).  In 
a  few  minutes  the  formation  of  the 
myelin  drops  begins  (Fig.  41,  10). 

No.  29. — The  Axis-cylinder. — 
Tea.se  dry  (like  No.  27  (/)  and  stain 
with    methylene    blue    { p.    34)  ;    the 

nodes  of    Ranvier  stain   first,  and  often  (■ic.  s6i.— Serve  fiukk  of  Rabbit.     X  560- 

so  deeply  that  the  axis-cylinder  cannot 

be  recognized  there.  The  axis-cylinder  frequently  shrinks  and  becomes  dis- 
]>laced  within  the  medullary  sheath,  or  it  contracts  and  becomes  convoluted. 
( )n  the  addition  of  glycerine  the  medullary  substance  can  no  longer  be  dis- 
tinctly recognized  as  such,  but  the  nuclei  of  the  neurilemma  are  often  rendered 
plainly  visible. 

No.  30. — E.yhihition  of  the  A.xis-iylinder  -luith  Chromic  Acid. — Kxpose  the 
sciatic  nerve  of  a  rabbit  recently  killed,  hciiig  careful  not  to  touch  it ;  place  a 
match-stick  parallel  to  the  long  axis  of  the  nerve,  and  secure  it  by  means  of 
ligatures  at  the  uj^per  and  lower  ends;  cut  the  nerve  on  the  further  side  of  each 
ligature,  and  place  it,  with  the  wood,  in  100  c.c.  of  a  o.  i  per  cent,  chromic- 
acid  .solution  (p.  20). 

In  about  24  hours  cut  the  ligatures  and  tease  a  piece  of  the  ner\e,  0.5  to 
I  cm.  long,  separating  it  into  bundles,  not  libers.  Put  the  bundles  back  into 
the  rhromic-acid  solution  :  in  24  hours  transfer  them  to  50  c.c.  of  distilled 
water,  and  in  2  to  3  hours  to  30  c.c.  of  gradually  strengthened  alcohols  to 
harden  (p.  29).  It  is  advantageous  to  leave  the  bundles  for  a  long  time,  i  to 
8  weeks,  in  90  per  cent,  alcohol,  as  they  are  then  more  readily  stained.      .After 


Node  of  R 
Biconical  enlar:gei 


252  HISTOLOGY. 

the  hardeniBg  is  completed,  the  bundles  are  to  be  teased  in  a  drop  of  picro- 
carmine,  placed  in  the  moist  chamber,  and  after  the  staining  is  completed, 
(which,  according  to  the  length  of  time  the  tissue  was  allowed  to  harden  in  the 
alcohol,  requires  from  3.^  to  3  days)  preserved  in  acidulated  glycerine  (p.  41). 
The  nodes  of  Ranvier  are  not  as  distinct  as  in  fresh  and  in  osmic-acid  prepara- 
tions, but  appear  as  delicate  transverse  lines  (Fig.  261).  The  somewhat 
shrunken  axis-cylinder  and  the  nuclei  are  stained  a  fine  red.  The  intensity 
of  the  color  depends  on  the  quality  of  the  picrocarmine,  which  unfortunately 
varies  greatly. 

No.  31. — Nodes  of  Ranvier  and  Axis-cylinders. — Add  10  c.c.  of  a  i  per 
cent,  solution  of  silver  nitrate  to  20  c.c.  of  distilled  water.  Kill  a  frog,  open 
the  abdomen  by  a  crucial  incision,  turn  out  the  viscera,  and  expose  the  nerves 
descending  on  either  side  of  the  vertebral  column.  Wash  out  the  abdominal 
cavity  with  distilled  water,  and  pour  over  the  nerves  about  one-third  of  the 
silver  solution,  .\fter  two  minutes  carefully  cut  out  the  delicate  nerves,  put 
them  for  a  half-hour  in  the  remainder  of  the  silver  solution,  placing  them  in 
the  dark.  Then  transfer  them  to  10  c.c.  of  distilled  water,  in  which  they  may 
remain  for  from  i  to  24  hours.  If  the  nerves  are  now  examined  in  a  drop  of 
water,  with  the  low  power,  the  endothelial  sheath  of  the  nerve  and  numerous 
pigment-cells  will  be  seen  ;  frequently  a  blood-vessel  lies  along  the  nerve.  On 
examination  with  the  high  power,  little  will  be  seen  of  the  nodes  and  axis- 
cylinders,  but  if  the  preparation  be  exposed  for  several  hours  to  daylight  (or  a 
{liw  minutes  to  sunlight)  the  reaction  takes  place  and  the  parts  mentioned  be- 
come silvered.  The  biconical  swelling  on  the  axis-cylinder  often  becomes  dis- 
placed in  teasing,  and  cannot  always  be  readily  found  by  the  beginner  (Fig.  42). 

No.  32. — Nonmedullated  Nerz'e-fibers. — Tease  a  portion  of  the  pneumo- 
gastric  nerve  of  a  rabbit  on  a  dry  slide  (No.  27  a),  and  add  a  few  drops  of  a 
yi,  per  cent,  osmic-acid  solution  ;  in  5  to  10  minutes  the  meduUated  nerve-fibers 
become  blackened  (which  may  be  ascertained  by  examination  with  the  low 
power).  Remove  the  osmic-acid  solution  and  add  a  few  drops  of  distilled 
water,  which  should  be  renewed  in  5  minutes.  In  5  minutes  more  remove  the 
water,  add  a  few  drops  of  picrocarmine,  apply  a  cover-glass,  and  place  in  the 
moist  chamber  for  from  24  to  48  hours  ;  then  displace  the  picrocarmine  with 
acidulated  glycerine  (p.  41).  The  tissue  may  be  teased  again  after  the  staining 
is  completed,  which  is  now  more  easily  done  because  the  elements  are  more  dis- 
tinctly seen.  With  high  magnification  the  medullated  nerve-fibers  appear  blue- 
black,  the  nonmedullated  pale  gray  and  finely  striated  longitudinally.  The 
sympathetic  nerve  treated  in  the  same  way  exhibits  more  numerous  non- 
medullated nerve-fibers.  But  this  nerve  is  somewhat  more  difficult  to  find. 
Cut  through  the  greater  cornu  of  the  hyoid  bone,  also  the  hypoglossal  nerve,  and 
push  them  aside  ;  behind  the  pneumogastric  nerve  lies  the  sympathetic,  which 
may  be  recognized  by  its  3  to  4  mm.  in  size,  ellipsoidal,  yellowish,  and  trans- 
parent superior  cervical  ganglion.  If  the  piece  of  the  nerve  lying  close  under 
the  ganglion  be  teased,  ganglion-cells,  the  majority  of  which  contain  two  nuclei, 
will  be  obtained  ;  it  is  difficult  to  isolate  the  cells  so  that  their  processes  can  be 
seen.  In  Fig.  41,  accideutallv,  only  the  more  unusual  uninucleated  ganglion- 
cell  is  to  be  seen. 

VI.   THE  HEART  AND  THE  BLOOD-VESSELS. 

No.  33.  —  The  Heart  and  the  Large  Blood-vessels. — Cut  out  a  papillary 
muscle  from  a  human  heart,  a  piece  of  the  aorta  2  cm.  long,  a  piece  i  to  2 
cm.  long  of  the  bronchial  arterv  with  its  veins  and  tlie  surrounding  connective 


SPECIAL    TECHNIQUE.  283 

tissue,  and  a  piece  of  the  renal  vein  i  cm.  long,  and  suspend  them  on  a 
thread  in  a  bottle  containing  40  c.c.  of  absolute  alcohol.  In  24  to  48  hours 
the  objects  are  ready  to  section.  Embed  them  in  liver  (the  artery  and  vein 
maybe  embedded  together  and  will  not  be  injured  by  strong  compression), 
cut  thin  cross-sections  and  stain  in  Bohmer's  hematoxylin  2  to  5  minutes 
(p.  31).  Mountindamar  (Fig.  43,45,47,  48,  49).  Theelastic  fibers  do  not 
stain,  but  with  the  high  power  can  often  be  distinctly  recognized. 

The  arrangement  of  the  elements  of  the  adventitia  cannot  be  satisfactorily 
appreciated  in  cross-sections — often  they  all  appear  to  be  circularly  disposed 
(a  portion  of  them  are  circularly  arranged — for  example,  those  of  the  inner- 
most strata  of  the  external  elastic  membrane).  The  exact  arrangement  can 
only  be  seen  in  longitudinal  sections,  which  al.so  show  the  muscle-fibers  of  the 
adventitia  plainl\ . 

No.  34. — Small  Blood-vessels  ami  Capillaries. — From  the  base  of  a  human 
brain  strip  off  slowly  ])ieces  of  the  pia  i  to  3  cm.  in  length  (in  this  way 
delicate  blood-vessels  that  penetrate  the  brain  vertically  are  obtained),  shake 
them  in  Miiller's  fluid  to  free  them  from  adherent  fragments  of  brain-tissue, 
and  place  them  in  50  c.c.  of  Miiller's  fluid  for  from  3  to  10  days  ;  then  trans- 
fer them  for  from  i  to  3  hours  to  water  (for  i  hour  to  running  water),  and 
harden  them  in  about  40  c.c.  of  gradually  strengthened  alcohol  (p.  29). 
Kxamine  one  of  these  pieces  in  a  watch-glass  on  a  black  background,  and  it 
will  be  seen  that  small  vessels  are  isolated. 

a.  With  a  fine  scissors  cut  off  small  twigs  with  their  ramifications,  stain 
them  2  to  5  minutes  in  Bohmer's  hematoxylin  (p.  31)  and  mount  in  damar 
(Fig.  44)- 

b.  From  the  larger  twigs  of  the  cerebral  blood-vessels  cut  pieces  about 
5  mm.  long,  slit  them  open  lengthwise,  stain  them  in  Bohmer's  hematoxylin, 
and  place  them  on  the  slide  with  the  adventitia  side  down.  Mount  in  damar. 
By  changing  the  focus  the  three  coats  of  the  vessels  and  their  general  arrange- 
ment can  be  seen. 

Capillaries  may  also  be  found  on  examining  fresh  brain  tissue.  They  may  be 
recognized  by  their  parallel  outlines  and  the  oval  nuclei  of  their  endothelial 
cells;   they  may  be  found  in  other  preparations,  for  example  in  No.  9. 

No.  35. — Epithelium  (Endothelium)  of  the  Blpod-ressels. — Decapitate  a 
rabbit,  open  the  abdomen  by  a  crucial  cut  made  with  the  scissors ;  insert 
under  the  mesentery  a  cork  frame  about  2  cm.  square,  span  it  smoothly  over 
this  and  fasten  it  with  quills  or  hedge-hog  spines,  taking  care  to  touch  the 
memlirane  as  little  as  possible  with  the  fingers.  Cut  it  off  all  around  the 
frame  and  place  the  stretched  membrane  with  the  frame  in  20  to  30  c.c.  of  i 
per  cent,  silver  solution.  In  about  30  seconds  the  solution  becomes  turbid 
and  milky  ;  remove  the  frame,  carefully  wash  the  membrane  with  distilled 
water,  place  the  whole  in  a  white  capsule  containing  100  c.c.  of  distilled  water 
and  expose  it  to  direct  sunlight.  In  a  few  minutes  a  brown  coloration 
appears.  Now  transfer  the  whole  to  50  c.c.  of  70  per  cent,  alcohol  (the 
membrane  must  be  submerged  in  the  alcohol)  ;  in  a  half-hour  cut  out  small 
pieces,  5  to  10  mm.  long,  and  mount  them  in  damar.  In  the  absence  of  sunlight, 
take  the  preparation  from  the  silver  solution,  wash  it;  place  it  for  about  20 
hours  in  about  30  c.c.  of  70  per  cent,  of  alcoliol,  then  in  a  like  quantity  of  90 
per  cent,  alcohol,  and  expose.it  to  sunlight  on  the  first  opportunity.  It  must  not 
l)e  forgotten  that  the  whole  blood-vessel  and  not  a  section  of  it  is  present,  so 
that  in  order  to  obtain  a  view  such  as  that  in  Fig.  46,  the  surface  of  the  vessel 
must  be  in  focus. 


284  HISTOLOGY. 

No.  36. — Elastic  Fenestrated  Membranes. — See  Techn.  No.  13. 

^'o-  37- — Development  of  Ca/'tllaries. — Chloroform  a  seven-days' -old 
rabbit,  fasten  it  with  pins  on  a  cork-plate,  open  the  abdomen  by  a  crucial 
incision,  quickly  remove  the  spleen,  stomach,  and  attached  greater  omentuui 
and  place  these  parts  in  80  c.c.  of  a  saturated  aqueous  solution  of  picric  acid 
(p.  20).  In  this  solution  the  omentum,  otherwise  difficult  to  separate,  spreads 
out  easily.  After  i  hour  cut  it  off,  transfer  it  to  60  c.c.  of  distilled  water,  and 
divide  with  the  scissors  into  pieces  about  i  cm.  square.  Place  such  a  piece  on 
a  dry  slide  (remove  the  water  with  filter-paper)  and  with  needles  spread  it  out 
as  smooth  as  possible,  which  is  the  more  easily  done,  the  less  moisture  there  is 
present.  Put  i  to  2  drops  of  Bohmer's  hematoxylin  on  the  preparation.  In 
from  I  to  5  minutes  drain  off  the  hematoxylin  and  place  the  slide  with  the  pre- 
paration in  a  flat  dish  containing  distilled  water  ;  the  membrane  will  soon 
float  from  the  slide,  but  will  remain  smooth,  and  in  5  minutes  should  be  trans- 
ferred with  the  section-lifter  to  a  watch-glass  containing  eosin  (p.  23),  in  which 
It  should  remain  3  minutes.  It  should  then  be  washed  for  i  minute  in  distilled 
water  and  placed  on  a  slide  ;  the  water  should  be  absorbed  with  filter-paper,  any 
wrinkles  smoothed  out  with  needles,  and  a  cover-glass  with  a  drop  of  dilute  gly- 
cerine suspended  from  its  lower  surface  applied.  The  preparation  may  be 
mounted  in  daraar  instead  of  glycerine  (that  is,  dehydrated  in  absolute  alcohol, 
cleared  in  oil  of  bergamot,  and  then  mounted  in  damar),  but  the  finer  struc- 
tural details  are  apt  to  be  lost.  The  colored  blood-corpuscles  are  stained  a 
bright  red  by  the  eosin  (Fig.  50). 

In  spreading  out  the  membrane  on  the  slide,  delicate  young  capillaries  may 
be  easily  torn  loose  from  the  older  capillaries  and  then  simulate  "  isolated  cells 
containing  blood-corpuscles  ;  "  such  artificial  products  have  been  described  as 
"  vasoformative  cells. ' ' 

VII.   THE  BLOOD. 

No.  38. — Colored  Blood-corpuscles  of  Man. — Carefully  cleanse  a  slide  and 
a  small  cover-glass  (finally  with  alcohol).  With  a  clean  needle  prick  the  tip 
of  the  finger,  at  the  side  ;  with  the  cover-glass  lightly  touch  the  first  drop  of 
blood  that  exudes,  and  without  the  addition  of  any  reagent  place  it  imme- 
diately on  the  slide.  With  the  high  power  many  colored  corpuscles  adhering 
to  one  another  by  their  broad  surfaces,  forming  the  so-called  rouleaux,  may  be 
seen,  as  well  as  isolated  colored  and  colorless  blood-corpuscles.  The  distor- 
tion of  many  of  the  colored  corpuscles  is  due  to  evaporation  ;  the  corpuscles 
are  beset  with  minute  spines,  a  condition  which  is  known  as  crenation.  If  a 
drop  of  water  be  placed  at  the  edge  of  the  cover-glass,  the  corpuscles  soon  become 
decolorized  and  the  water  acquires  a  yellowish  tinge  ;  the  corpuscles  become 
spherical,  have  the  appearance  of  pale  circles,  and  finally  disappear  entirely. 
The  student  is  advised  to  study  the  decolorization  of  a  single  corpuscle.  In 
Fig.  51,  6,  the  tinged  area  surrounding  the  bleached  corpuscles  is  somewhat  too 
deeply  shaded. 

No.  39. — Permanent  preparations  of  colored  cind  colorless  blood-corpuscles 
are  made  by  Ehrlich's  dry  method.  The  method  accurately  carried  out,  after 
some  practice,  yields  good  results,  but  with  unskilful  manipulation  many  cari- 
catures arise  and  mislead  the  inexperienced.  The  employment  of  this  method 
for  purposes  of  investigation  and  discovery  re.quires  great  skill  and  great 
caution  in  judgment. 

Preliminary  Manipulations. — For  each  preparation  two  thin  cover-glasses 
are  required  (they  must  not  be  over  o.i  mm.   thick).      Place  them  for  a  few 


SPECIAL   TECHNIQUE.  285 

minutes  in  dilute  hydrochloric  acid,  then  in  distilled  water,  and  finally  in 
alcohol.  It  is  best  to  take  cover-glasses  that  have  never  been  used.  Prepare 
a  mixture  of  equal  parts  of  absolute  alcohol  and  ether  (about  5  c.c.  of  each). 
Cleanse  the  tip  of  the  finger  first  with  soap  and  water,  and  then  with  a  tuft  of 
clean  cotton-wool  moistened  in  the  alcohol-ether  mixture.  With  a  clean  needle 
(not  previously  used  for  anatomic  purposes)  prick  the  pad  of  the  finger,  made 
slightly  hyjieremic  by  compression  ;  take  up  a  cover-glass  with  the  forceps  (not 
with  the  fingers)  press  it  lightly  upon  the  blood  that  exudes,  and  place  it  on 
the  second  cover-glass,  with  one  edge  projecting  slightly.  The  drop  of  blood 
will  spread  out  in  a  thin  film  between  the  two  glasses,  which  are  then  slipped 
apart  by  means  of  two  forceps.  By  this  manipulation  the  influence  of  the 
insensible  perspiration  on  the  blood -corpuscles  is  prevented,  which  otherwise 
would  shrink  or  lose  their  hemoglobin. 

Exposed  to  the  air,  the  blood  on  the  cover-glasses  dries  in  a  few  minutes  : 
the  glasses  are  then  to  be  placed  in  the  alcohol-ether  mixture  for  fixation.  In 
from  ]l  to  2  hours  they  should  be  removed,  dried  again  in  the  air,  when  they 
are  ready  for  further  treatment,  which  may  be  applied  immediately  or  later, 
since  the  preparations  thus  fixed  may  be  preserved  for  a  long  time. 

a.  O.xyphile  {Eosinop/ii/f,  a)  Granules. — Place  the  cover-glass  prepara- 
tion for  24  hours  in  about  4  c.c.  of  distilled  water,  to  which  about  10  drops  of 
eosin  solution  have  been  added.  Rinse  i  minute  in  distilled  water  and  stain 
1  to  5  minutes  in  a  watch-glass  with  hemalum  (p.  32).  Transfer  to  distilled 
water ;  remove  in  5  minutes  and  let  the  preparation  dry  in  air  under  a  bell- 
glass.  Mount  in  damar.  The  colored  blood-corpuscles  and  the  oxyphile 
granules  of  the  colorless  corpuscles  are  stained  a  bright  red,  the  nuclei  are 
blue.  The  oxyphile  granules  occur  in  the  leucocytes  of  normal  blood,  of  the 
Ivmph,  and  in  the  tissues,  but  are  uncommon  in  normal  blood.  A  magnifica- 
tion of  400  diameters  is  sufficient  to  find  them. 

/'.  Basophik  Granules. — Two  groups  are  distinguished,  the  ^-granules  and 
the  o-granules.  The  ygraniiles  (Masfzellen  Granulationen),  which  occur  only 
in  the  leiicocytes  of  pathologic  blood,  are  to  be  stained  according  to  the  method 
given  in  No.  6.  When  the  staining  is  completed,  proceed  as  in  a.  The  blue- 
violet  granules  are  coarser  than  the — 

<i-granules,  which  occur  in  the  round  nucleated  leucocytes  of  normal  and 
other  blood.  Stain  the  cover-glass  preparation  5  to  10  minutes  in  5  c.c.  of 
methylene  blue  solution  (p.  23),  wash,  dry,  and  mount  in  damar.  These  gran- 
ules are  minute  and  .scarcely  to  be  seen  with  the  usual  high-power  dry  lenses ; 
an  immersion  lens  should  be  used.  In  staining  with  methylene  blue  not 
infrequently  the  film  of  blood  floats  from  the  cover-glass;  this  may  be  pre- 
vented by  passing  the  dry  cover-glass  preparation  rapidly  through  a  flame  be- 
fore staining. 

c.  Neiitrophile  (s-)  Granules. — Dissolve  (i)  i  gm.  of  orange-yellow 
extra  in  50  c.c.  of  distilled  water  ;  (2)  i  gm.  of  acid  fuchsin  extra  in  50  c.c. 
of  distilled  water;  (3)  i  gm.  of  crystallized  methyl-green  in  50  c.c.  of 
distilled  water,  and  let  the  three  solutions  settle.  Then  mix  11  c.c.  of  solu- 
tion (i)  with  10  c.c.  of  solution  (2),  and  add  20  c.c.  of  distilled  water  and 
10  c.c.  of  distilled  alcohol;  to  this  mixture  add  a  mixture  of  13  c.c.  of  solution 
(3),  10  c.c.  of  distilled  water,  and  3  c.c.  of  absolute  alcohol.  The  whole  should 
then  he  allowed  to  stand  for  from  i  to  2  weeks.  In  this  ••  triacid-solution  "  the 
cover-glass  should  be  placed  for  15  minutes,  then  washed,  dried,  and  mounted 
in  damar.  The  neutrophile  granules,  which  are  found  in  the  leucocytes  with 
lobiilated  nuclei  in  normal  and  other  blood,  are  of  a  violet  color,  and  are  easily 
seen  with  the  usual  dry  high-power  lenses  ;  the  oxy])hile  granules  and  the 
colored  blood -corpuscles  are  of  a  yellow-brown  or  chocolate-brown  color,  the 


2  so  HISTOLOGY. 

nuclei  a   bright  blue-green,  though  their  outlines  are  not  so  distinct  as  in  the 
hemalum  preparation. 

No.  40. — Blood-platelets. — -Mix  about  5  drops  of  an  aqueous  solution  of 
methyl-violet  (p.  23)  with  about  5  c.c.  of  salt  solution  (p.  19).  Filter  the 
mixture  and  place  a  drop  of  it  on  the  tip  of  the  finger ;  prick  the  finger  through 
the  drop  ;  the  blood  as  it  exudes  mixes  with  the  methyl-violet ;  take  up  a  drop 
of  it  with  the  cover-glass,  and  examine  with  the  high  power.  The  platelets  are 
stained  an  intense  blue,  are  of  a  peculiar  luster,  disk-shaped,  and  not  to  be 
confused  with  the  white  corpuscles,  likewise  stained  blue  (Fig.  51).  They  are 
numerically  variable  elements,  occurring  in  large  numbers  in  the  blood  of  one 
individual,  while  in  the  blood  of  another  they  are  only  to  be  found  singly  here 
and  there.  Care  must  be  taken  not  to  confuse  them  with  foreign  particles, 
which  may  occur  even  in  the  filtered  staining  solution. 

No.  41.  —  Colored  Blood-corpuscles  of  the  Frog. — Prepare  the  slide  and 
treat  the  blood  like  No.  38. 

No.  42. — For  Legal  Purposes. — Since  it  is  usually  dried  blood  that  is  to 
be  examined,  dissolve  small  particles  of  dried  blood  in  35  per  cent.  i)otash  solu- 
tion on  a  slide;  blood-stained  ])ieces  of  linen  may  be  teased  in  a  drop  of  the 
same  solution.  Although  the  colored  blood-corpuscles  of  domestic  mammalian 
animals  are  smaller  than  those  of  man,  it  is  nevertheless  impossible  from  the 
size  of  the  blood-cell  to  determine  its  source.  On  the  other  hand,  it  is  easy  to 
distinguish  the  disk-shaped  corpuscles  of  mammals  from  the  oval  elements  of 
other  vertebrates. 

No.  43. — Colorless  Blood-corpuscles,  Leucocytes  in  Motion. — Preliminary 
manipulations  :  carefully  cleanse  a  slide  and  cover-glass  with  alcohol.  Kill  a 
frog,  grasp  it  by  its  hind  legs,  dry  its  back  somewhat  with  a  cloth,  and  with 
fine  scissors  make  an  incision  i  cm.  long  parallel  to  and  close  beside  the  vertebral 
column.  Introduce  a  capillary  pipette  into  the  wound  (with  the  tip  directed 
forward)  and  suck  the  tip  full.  A  small  drop  is  sufficient ;  blow  it  on  to  the 
slide,  cover  it  quickly,  and  seal  the  edges  with  mehed  paraffin  (p.  41). 
Such  a  preparation  shows  colored  and  colorless  blood-cells  ;  at  first  the  nuclei 
of  the  former  are  indistinct.  The  nuclei  of  the  living  colorless  blood-corpuscles 
are  in  general  not  to  be  seen.  For  the  study  of  amceboid  movement,  select 
leucocytes  who,se  protoplasm  is  partly  granular  and  that  are  not  spherical.  The 
movements  are  slow;  of  this  one  may  convince  one's  self  by  studying  a  sin- 
gle leucocyte  and  making  sketches  of  it  at  intervals  of  from  i  to  2  minutes. 
Study  with  the  high  power  (Fig.  4). 

No.  44. — Blood  Ciystals. — a.  .^if;///// rryj/rtA- are  easily  obtained.  Cut  a 
small  strip,  about  3  mm.  long,  from  a  piece  of  linen  previously  saturated  with 
blood  and  dried,  and  place  it  with  a  pinhead-sized  crystal  of  common  salt  on 
a  clean  slide  ;  add  a  large  drop  of  glacial  acetic  acid,  and  with  a  glass  rod  stir 
the  linen  and  salt  until  the  acid  acquires  a  brownish  tinge.  This  must  be  done 
rapidly,  lest  the  acetic  acid  evaporate.  Heat  the  slide  over  a  flame  until  the 
fluid  boils  up  once  (this  may  be  most  readily  seen  near  the  strip  of  linen). 
Remove  the  linen  and  examine  the  dry  brown  places  on  the  slide  with  the  high 
power  (from  240  diameters  up).  Occasionall)'  the  brown  crystals  may  be  seen 
without  the  cover-glass  and  without  a  mounting  medium,  lying  next  to  numerous 
fragments  of  white  salt  crystals  (Fig.  53,  i).  To  preserve,  add  a  large  drop  of 
damar  and  apply  a  cover-glass.  The  hemin  crystals  vary  greatly  in  form  and 
size.  In  the  same  slide  well-developed  crystals  lying  singly,  crosswise  over  one 
another,  or  in  stellate  groups  may  be  seen,  with  whetstone  shapes  and  minute  par- 


SPECIAL    TECHNIQUE.  287 

tides  that  scarcely  exhibit  crystallization.  The  demonstration  of  the  hetnin 
crystals  is  of  great  importance  in  forensic  cases.  While  it  is  easy  to  exhibit 
the  crystals  in  large  stains  on  wearing  apparel,  it  is  difficult  when  the  stains 
are  small,  and  especially  on  rusty  iron,  to  prove  that  they  are  from  blood. 
The  instruments  and  reagents  employed  in  such  investigations  must  be  abso- 
lutely free  from  contamination. 

h.  Hematoidin  crystals  are  obtained  by  teasing  old  blood  extravasations  ; 
they  can  be  recognized  macroscopically  by  their  reddish-brown  color  (in  the 
corpus  luteum,  in  cerebral  hemorrhages). 

c.  Hemoglobin  crystals  may  be  obtained  by  transferring  5  c.c.  of  the  blood 
of  a  dog  to  a  test-tube,  adding  a  couple  of  drops  of  ether,  and  shaking  vigor- 
ously until  the  blood  becomes  lake-colored.  Then  spread  a  drop  on  a  slide 
and  let  the  prei)aration  dry  in  the  cold.  When  crystallization  has  occurred, 
add  a  drop  of  glycerine  and  apply  a  cover-glass.  The  large  crystals  often  ex- 
hibit a  tendency  to  split  lengthwise  (Fig.  53,  4  a). 


VIll.   THK  LYMPHATIC  SVSTKM. 

No.  45. — Lymph-vessels. — For  the  study  of  the  walls  of  the  larger  lymph- 
vessels  select  the  vessels  opening  into  the  inguinal  glands,  that  are  large 
enough  to  be  taken  out  with  the  forceps  and  scalpel.  Prepare  like  the  large 
blood-vessels,  No.  33  or  No.  34  b. 

No.  46. — For  the  representation  of  the  more  delicate  lymph-vessels,  their 
course  and  arrangement,  the  method  of  interstitial  injection  is  often  employed. 
The  needle  of  a  hypodermic  syringe  filled  with  Berlin-blue  is  thrust  haphazard 
into  the  tissue  ;  this  is  a  crude  method,  the  results  of  which  are  of  very  doubt- 
ful value.  P>en  though  here  and  there  actual  lymph-vessels  may  be  thus  filled, 
in  most  ca.ses  the  injection-mass  is  simply  driven  forcibly  into  the  interfascicu- 
lar clefts  of  the  connective  tissue.  From  this  the  value  of  any  decision  with 
regard  to  "  lyniph-ves.sels  "  and  "lymph-spaces"  thus  exhibited  may  be 
inferred. 

No.  47. — Lymph-nodes. — For  a  general  view  the  mesenteric  glands  of 
kittens  are  suitable.  For  fixation  and  hardening  place  them  in  30  c.c.  of  abso- 
lute alcohol  ;  in  three  days  thin  sections  can  be  readily  made,  and  should  be 
taken  so  that  they  pass  through  the  hilus,  which  may  be  easily  recognized  macro- 
.scopically  by  an  external  depression.  Longitudinal  sections  passing  through 
the  poles  of  the  node  are  best,  though  transverse  sections  are  also  useful. 
Stain  6  to  8  sections  in  Bcihmer's  hematoxylin  for  from  2  to  3  minutes,  then  in 
eosin,  at  the  most  i  minute  (p.  32,  3  /<),  then  transfer  them  to  a  test-tube  half 
filled  with  distilled  water  and  shake  them  for  from  3  to  5  minutes.  Pour  the 
shaken  sections  into  a  flat  dish  ;  the  cortex  and  medulla  can  be  distinguished 
macroscopically  by  the  uniformly  blue  color  of  the  former  and  the  variegated 
appearance  of  the  latter.  Mount  in  damar.  With  the  lower  |)Ower  fields 
similar  to  that  in  Fig.  55  may  be  seen  in  favorable  places.  The  trahecuhne  are 
but  slightly  developed.  The  adipose  tissue  adhering  to  the  nodes  must  not  be 
taken  for  reticular  tissue.  High  magnification  is  of  no  advantage;  the  sharp 
outlines  disappear  and  the  picture  loses  in  distinctness. 

No.  48. — Lymph-nodes  of  mature  animals  and  of  man  are  difficult  to 
understand,  because  the  entire  cortex  is  transformed  into  a  continuous  mass 
sprinkled  with  irregular  germinal  centers.  In  shaking  the  sections  the  germinal 
centers  are  apt  to  fall  out,  and  leave  round  spaces  recognizable  macroscopically. 
The  lymph-sinuses  can  only  be  indistinctly  made  out.     The  mesenteric  fol- 


288  HISTOLOGY. 

Holes  of  the  ox  are  well  adapted  for  the  representation  of  the  network  of  the 
mcdiillaty  cords  and  trabecula.  Place  pieces  2  cm.  long  in  200  c.c.  of  concen- 
trated aqueous  picric-acid  solution,  and  after  24  hours,  with  a  sharp  knife  moist- 
ened with  water,  endeavor  to  cut  thin  sections.  This  is  not  so  easily  done  as 
after  alcohol  fixation,  but  slightly  thicker  sections  can  be  used.  Place  the  sec- 
tions for  one  hour  in  100  c.c.  of  distilled  water,  which  must  be  changed  fre- 
quently, then  stain  with  Bohmer's  hematoxylin  and  eosin  and  shake  them  (see 
No.  47).  Mount  in  damar  (p.  38).  The  trabeculse  are  red,  the  medullary 
cords  blue  ;  with  low  magnification  the  appearance  of  the  section  is  like  Fig. 
56  ;  with  high  magnification  the  reticular  connective  tissue  of  the  lymph-sin- 
uses can  be  seen  ;  the  majority  of  the  leucocytes  occupying  the  meshes  become 
loosened  by  tiie  treatment  with  picric  acid  and  lost  in  the  shaking. 

No.  49. — Elements  of  the  Spleen. — Make  an  incision  through  a  fresh 
spleen  ;  with  a  scalpel  obliquely  applied  scrape  the  cut  sm-face  and  examine  a 
little  of  the  red  mass  adhering  to  the  blade  in  a  drop  of  salt  solution.  Use  the 
high  power.  Often,  especially  in  animals,  only  colored  and  colorless  blood- 
corpuscles  are  found  ;  some  of  the  latter  contain  minute  granules.  In  human 
spleens,  in  addition  to  the  numerous  colored  blood-corpuscles  altered  in  form,  en- 
dothelial cells  of  the  blood-vessels  maybe  found  :  the  latter  were  formerly  called 
"spleen-fibers"  (Fig.  58,  2,  3).  In  many  human  spleens,  multinucleated  cells 
and  cells  containing  colored  blood-corpuscles  often  cannot  be  found  (Fig.  58,  4). 

No.  50. — The  Spleen. — Without  cutting  it,  fix  the  entire  spleen  in 
Mailer's  fluid,  using  one  liter  for  a  human,  200  to  300  c.c.  for  a  cat's  spleen. 
After  2  weeks  for  the  cat's,  5  weeks  for  the  human  spleen,  wash  for  from  i  to  2 
hours  in,  if  possible,  running  water,  cut  out  pieces  2  cm.  square  and  harden 
them  in  60  c.c.  of  gradually  strengthened  alcohol  (p.  29).  Sections  not  too 
thin  are  to  be  stained  in  Bohmer's  hematoxylin  and  mounted  in  damar.  If  it  is 
desired  to  stain  the  trabecule,  after  staining  in  hematoxylin  is  completed  place 
the  sections  for  y^  minute  in  eosin.  In  successful  preparations  the  pulp  and  the 
Malpighian  bodies  are  blue,  the  trabeculse  rosy,  the  vessels,  distended  with  blood- 
corpuscles,  brown.  If  the  staining  in  eosin  be  prolonged  beyond  30  seconds 
the  blood-corpuscles  become  brick-red,  the  trabecular  dark  red,  and  the  distinc- 
tion between  them  is  apt  to  be  lost.  The  sections  are  most  satisfactory  when 
examined  with  a  very  low  power  (Fig.  57)  ;  with  the  high  power  the  outlines 
are  often  indistinct. 

No.  51. — Reticular  Connective-tissue  of  the  Spleen. — Shake  a  thin  sec- 
tion fixed  and  stained  like  No.  50  for  about  5  minutes  in  a  test-tube  half  filled 
with  distilled  water.  Mount  in  glycerine.  The  leucocytes  are  difficult  to  dis- 
lodge ;  the  narrow-meshed  network  can  only  be  seen  at  the  edges  of  the 
preparation  (Fig.  59). 

No.  52. — Karyoinitotie  Figures  in  the  Spleen  and  Lymph-nodes. — For  this 
purpose  small  pieces  (5  to  10  mm.  long)  of  Tvarm  living  spleen  and  lymph-node 
should  be  fixed  in  chromo-aceto-osmic  acid  (p.  21),  and  hardened  in  alcohol. 
Stain  thin  sections  in  saffranin  (p.  33).  Mount  in  damar.  The  karyomitotic 
figures  of  mammals  are  so  small  that,  with  the  usual  magnification  (560  diam- 
eters), they  can  only  be  found  by  the  practiced  microscopist.  They  may  be 
recognized  by  their  deep  red  color  (Fig.  60). 

No.  53. — Blood-vessels  of  the  Spleen  may  be  obtained,  incidentally,  by 
injecting  the  stomach  and  intestine  (compare  with  No.  no). 

No.  54.  Nei-t'cs  of  Spleen. — For  this  purpose  the  spleen  of  the  mouse  is 
best  suited.     Halve  it,  and  apply  Golgi's  method  for  demonstration  of  the  ele- 


SPECIAL    TECHXIlJUE.  289 

merits  of  the  nervous  system  (p.  35).  It  is  sometimes  sufficient  to  place  the 
object  in  the  osmio-bichromate  mixture  (in  a  warm  chamber)  for  3  days  and 
for  the  same  length  of  time  in  the  silver  solution  ;  often  a  repetition  of  the 
whole  process  once  or  twice  yields  good  results. 

IX.     BONE. 

No.  55. — Dried  Bone. — The  bone  must  not  be  dried  before  maceration, 
but  must  be  placed  fresh  for  several  months  in  water,  which  should  be  fre- 
quently changed.  Then  it  is  to  be  dried  and  a  piece  held  between  two  pieces  of 
cork  or  cloth  clamped  in  a  vice,  and  with  a  compass-saw  sections  i  to  2  mm. 
thick,  transverse  or  longitudinal,  are  to  be  cut.  Secure  a  section  with  sealing- 
wax  to  the  under  surface  of  a  cork -stopper,  dip  the  whole  for  a  moment  in  water 
and  then  file  it,  first  with  a  coarse,  then  with  a  fine  file,  until  it  is  perfectly 
smooth  :  the  file  must  be  dipped  in  water  frequently,  in  order  to  wash  off 
the  adherent  particles  of  bone  and  to  prevent  the  heating  of  the  sealing-wax 
by  friction. 

The  section  of  bone  should  then  be  loosened  by  heating  the  sealing-wax,  and 
the  smooth  side  stuck  fast  to  the  stopper.  It  must  now  be  filed  until  it  is  so  thin 
that  the  sealing-wax  can  be  seen  through  it.  The  whole  should  then  be  placed  in 
90  per  cent,  alcohol,  in  which  within  a  few  minutes  the  section  becomes  loosened 
from  the  cork.  Moisten  a  coarse  whetstone  with  water,  rub  it  with  a  second  whet- 
stone until  the  surface  is  covered  with  a  little  grinding-paste  ;  lay  the  section 
in  it,  place  a  smooth  cork  upon  it  (one  without  cracks),  and  with  a  circular 
motion  grind  it  on  both  sides  ;  it  is  not  necessary  to  glue  the  section  to  the 
cork.  The  section  when  sufficiently  thin  is  transparent ;  this  is  to  be  ascer- 
tained by  drying  it  between  pieces  of  filter-paper  and  examining  with  the  low 
power.  It  should  then  be  ground  on  a  fine  whetstone,  in  the  .same  manner 
as  on  the  coarse,  and  when  both  sides  are  smooth,  dried  with  filter-pa|jer 
and  polished.  To  do  the  latter,  nail  a  piece  of  wa.sh-leather  smoothly  on  a 
board,  sprinkle  it  with  chalk,  and  with  the  tip  of  the  finger  rub  the  section  to 
and  fro  on  it.  In  this  way  the  previously  dull  section  acquires  shining  sur- 
faces. The  adherent  powder  may  be  removed  by  rubbing  the  section  on  fresh 
wash-leather.  The  finished  section  is  to  be  placed  dry  on  a  slide  and  the 
cover-gla.ss  secured  by  means  of  cement  (  p.  38). 

Examine  first  with  the  low,  then  with  the  high  power.  (If  the  section  is 
thick,  it  may  be  impossible  to  e.xamine  it  with  the  high  power,  since  then  the 
objective  cannot  be  brought  near  enough  to  the  preparation.)  The  bone 
lacunae  and  bone  canaliculi  are  filled  with  air.  and  with  the  customary  illumi- 
nation of  the  object  from  below  aj^pear  black  (Fig.  28). 

No.  56. — Sharpcy' s  I-il>eis. — Pre]»re  a  cross-section  of  the  middle  of  the 
shaft  of  a  tubular  bone,  preferably  of  a  young  individual,  according  to  the 
method  given  in  No.  55.  Place  the  finished  dry  section  for  from  2  to  5 
minutes  in  4  c.c.  of  turpentine  and  then  mount  in  dainar.  The  fibers,  invisi- 
ble in  the  sections  produced  by  other  methods  (No.  55  and  57),  can  be  plainly 
seen,  even  with  the  low  power  (  Fig.  66). 

No.  57. — Haversian  Canals  and  Lamellm. — Select  the  metacarpal  bone  of 
an  adult  ;  after  4  weeks'  fixation  in  Miiller's  fluid,  and  hardening  in  alcohol, 
decalcify  in  nitric  acid  (p.  29),  harden  again,  and  cut  transverse  and  longi- 
tudinal sections.  The  compact  structure  of  larger  bones  (the  femur,  for  ex- 
ample) require  too  much  time  (several  weeks)  for  decalcification.  The  jieri- 
osteum  should  be  allowed  to  remain  on  the  bone.  For  longitudinal  views 
of  Haversian  canals  very  thick  sections  (0.5  mm.  and  more)  must  be  cut. 
•9 


290  HISTOLOGY. 

Mount  in  dilute  glycerine  (Fig.  63).  Neither  are  very  thin  sections  neces- 
sary for  transverse  views  and  lamellar  systems ;  the  lamellae  are  best  seen  if  the 
section  be  examined  in  a  drop  of  distilled  water  and  the  mirror  turned  so 
that  the  object  is  only  half  illuminated  ;  thus,  too,  the  strife  produced  by 
the  bone  canaliculi,  running  vertical  to  the  lamellae,  are  best  seen  (Fig.  64). 
Mount  in  dilute  glycerine ;  this,  however,  renders  the  lamellar  systems  par- 
tially indistinct.  Not  every  part  of  the  bone  exhibits  all  the  lamellar  systems  ; 
the  outer  and  also  the  inner  ground  lamellae  are  frequently  wanting.  In  sec- 
tions taken  near  the  epiphyses  the  continuation  of  the  compact  substance  into 
the  trabeculae  of  the  spongy  bone  may  be  seen.  The  bone  lacunae  and  bone 
canaliculi  are  much  less  distinct  in  moist  preparations  than  in  dried  ground 
sections,  because  the  contained  air  has  been  displaced  by  the  mounting  medium. 
(Compare  Fig.  28  and  29.) 

Not  infreciuently  the  concentric  lamellae  of  the  Haversian  systems  are 
found  to  be  interrupted  by  an  irregular  line.  Up  to  this  line  the  osseous  tis- 
sue previously  formed  has  been  again  resorbed.  All  that  which  lies  within 
the  line  is  newly-deposited  bone-substance.  These  formations  are,  therefore, 
partially  filled  Haversian  spaces  (Fig.  64,  h). 


o  ® 


9 


^ 


:  262.— Isolated  Elements  o 

V  Fresh  Bonf-marrow 

FROM  A  Vertebra  of 

Calf.     X  560.     1.  In  salt 

solution.    2-  Stained  wiih  picrc 

.carmine.    3.  After  treatm 

ent  with  acidulaied  glyct 

:rine.    k.  Marrow-ceils;  >f, 

two  marrow-cells  containing  m 

a'^ses  of  pigment-granules 

,.  the  cell  on  the  right  se 

en  from  the  Mde.  the  cell  on 

the  lefi,  from  the  surface  ;  6,  no 

nnucleated  colored  blood-( 

lorpuscles  ;  r,  giant-cells 

;  in  the  one  oiil  he  right  the 

niiclr-u<i  is  dividing  by  constrict 

,ion,  and  two  of  the  future 

new  nuclei  are  seen  fror 

n  the  side,  another,  x,  from 

No.  58. — Red  Bone-marrow. — a.  Compress  the  vertebra  (cut  in  half)  or 
the  rib  of  a  calf  in  a  vice  or  with  tongs  ;  with  a  pipette  take  up  a  small  drop 
of  the  liquid  thus  expressed,  transfer  it  to  a  slide  and,  without  the  addition  of 
any  other  fluid,  apply  a  small  cover-glass,  or  better,  a  fragment  of  a  cover- 
glass.  Examined  with  the  high  power  red  blood-corpuscles,  hematoblasts, 
marrow-cells  of  different  sizes,  and  giant-cells  will  be  seen,  but  not  always  their 
nuclei  (Fig.  262,  i).  Add  a  drop  of  jaicrocarmine  (p.  41)  ;  the  nuclei  become 
red  in  from  i  to  2  minutes,  but  are  still  pale  (Fig.  262,  2).  If  the  picrocarmine 
is  displaced  by  salt  solution  and  then  by  dilute  acidulated  glycerine,  the  nuclei 
acquire  a  dee|3  color  and  sharp  contours  (Fig.  262,  3).  Occasionally  giant- 
cells  are  sought  in  vain.      Human  ribs  are  often  usable. 

b.  To  make  permanent  preparations,  proceed  as  follows  :  With  a  thin  cover- 
glass  take  up  a  drop  of  the  marrow  expressed  from  a  rib  and  make  two  cover- 
glass  preparations  as  directed  in  No.  39.  Since  the  marrow  does  not  diffuse  as 
readily  as  the  blood  between  the  two  cover-glasses,  make  slight  pressure  upon 
them  before  slipping  them  apart.  They  should  not  be  allowed  to  dry,  but 
should  be  placed  at  once  in  a  concentrated  aqueous  solution  of  sublimate  solu- 


SPECIAL    TECHNIQUE.  29  I 

tion  (5  gm.  in  loo  c.c.  of  distilled  water).  At  the  end  of  lo  minutes  transfer 
the  cover-glasses  to  20  c.c.  of  distilled  water,  which  is  to  be  changed  in  about 
5  minutes.  In  10  minutes  jjlace  them  in  5  c.c.  of  diluted  eosin  (p.  32,  3  b) 
for  from  i  to  5  minutes,  then  wash  for  a  moment  in  distilled  water  and  transfer 
them  to  5  c.c.  of  filtered  Bohmer's  hematoxylin  ;  after  i  to  2  minutes  place 
them  for  5  minutes  in  distilled  water  ;  remove  the  water  by  means  of  filter- 
paper  placed  at  the  edge  of  the  cover-glass,  and  place  them  in  absolute  alcohol 
(not  longer  than  i  minute,  lest  the  eosin  be  extracted),  then  in  pure  oil  of 
bergamot  for  3  minutes.  With  a  cloth  carefully  remove  the  oil  from  the  film- 
free  surface  of  the  cover-glass,  place  a  drop  of  damar  on  the  surface  containing 
the  film  of  marrow,  and  invert  the  cover-glass  on  a  slide.  The  colored  blood- 
corpuscles  and  the  ])rotoplasm  of  the  hematoblasts  are  stained  a  brilliant  red, 
the  protoplasm  of  the  remaining  cells  gray-violet ;  all  the  nuclei  are  blue.  Cells 
containing  oxyphile  (eosinophile)  granules  are  often  found  (Fig.  65).  The 
colored  blood-corpuscles  frequently  exhibit  distorted  forms. 

No.  59. — Articular  Cartilage. — Select  the  head  of  the  metacarpal  bone  of 
an  adult,  and  treat  it  according  to  the  method  given  in  No.  57.  Cut  longitudinal 
sections  and  mount  them  in  dilute  glycerine  (Fig.  67).  The  parallel  streaks 
often  present  in  the  hyaline  cartilage  are  produced  by  the  razor.  The  granules 
of  the  calcified  cartilage  have  disappeared  in  consequence  of  the  process  of 
decalcification  to  which  the  tissue  was  subjected. 

No.  60. — Synovial  Villi. — From  a  cadaver,  as  fresh  as  possible,  cut  out  a 
piece  about  4  cm.  long  of  the  capsular  ligament  at  the  edge  of  the  i)atella,  and 
with  the  scissors  cut  a  strip  2  to  3  mm.  broad  from  the  reddish,  glossy,  vel- 
vety inner  surface  of  the  same,  moisten  it  with  a  drop  of  salt  solution,  and 
without  a  cover-glass  examine  it  with  the  low  power.  At  the  edges  of  the 
tissue  the  villi  may  be  seen  ;  their  blood-vessels  often  still  contain  blood-cor- 
puscles. The  refractive  nuclei  of  the  endothelial  cells  lie  close  beside  one 
another  (Fig.  68). 

If  it  is  desired,  the  preparation  may  be  stained  under  the  cover-glass 
with  picrocarmine  and  mountetl  in  diluted  glycerine  (p.  41),  but  much  of  the 
original  beauty  is  thus  lost. 

No.  61. — Development  of  Bone. — Human  embryos  of  4  to  5  months, 
embryos  of  the  sheep,  jsig,  or  cow,  10  to  14  cm.  long  (measured  from  the  tip 
of  the  snout  to  the  root  of  the  tail),  are  suitable.  The  latter  may  be  ob- 
tained at  the  slaughter-house  ;  the  entire  uterus  should  be  ordered.  Place  the 
embryos  in  toto  (2  to  3  in  i  liter)  in  Miiller's  fluid  for  4  weeks;  the  fluid 
must  be  changed  fre(|uently.  Then  wash  in  running  water  i  to  6  hours, 
and  harden  in  200  to  400  c.c.  of  gradually  strengthened  alcohol  (p.  29). 
After  the  embryos  have  lain  i  week  or  longer  in  90  per  cent,  alcohol,  cut 
off  the  head  and  the  extremities,  close  to  the  rump,  and  decalcify  them  in  200 
c.c.  of  distilled  water,  to  which  2  to  4  c.c.  of  pure  nitric  acid  have  been  added. 
In  2  to  5  days,  during  which  the  decalcification  mediimi  must  be  changed 
about  three  times,  the  extremities  are  to  betaken  out  (the  head  is  probably  not 
yet  decalcified,  and  must  remain  in  2  per  cent,  nitric  acid  another  several  days) 
and  washed  1  to  6  hours  in  running  water,  and  again  hardened  in  gradu- 
ally strengthened  alcohol.  After  they  have  lain  5  days  in  90  i)er  cent,  alco- 
hol, cut  the  extremities  into  pieces  i  cm.  long,  which,  should  they  still  be  too 
soft,  may  be  placed  for  i  to  2  days  in  30  c.c.  of  absolute  alcohol. 

The  vertebra;  and  the  ribs  fiirnish  instructive  specimens. 

To  obtain  sections  showing  xhn  first  processes  in  the  develo])ment  of  bone, 
embed  in  liver  the  phalanges  and  metacarpal  bones  (the  latter  are  very  long  in 


292 


HISTOLOGY. 


the  animals  mentioned),  and  make  longitudinal  (sagittal)  sections,  from  the 
flexor  to  the  extensor  surface  ;  to  be  good  sections  must  be  taken  in  the  axis  of 
the  extremities ;  those  taken  from  the  margin  exhibit  pictures  that  are  not 
intelligible. 

For  mere  advajiccd  stages  make  chiefly  transverse  sections  of  the  humerus 
and  femur.  Sections  through  the  diaphysis  show  more  perichondral,  sections 
through  the  epiphyses  more  endochondral  bone. 

The  most  beautiful  examples  of  osteoblasts  may  be  obtained  in  cross-sections 
of  the  inferior  maxilla  ;  they  are  also  valuable  as  preparations  showing  the  devel- 
opment of  teeth. 

For  still  later  stages  the  skeleton  of  newborn  animals  is  useful  ;  their 
phalanges  show  tolerably  early  stages  in  the  process,  their  carpal  bones  the  first 
stages.     The  decalcification  requires  somewhat  more  time  (up  to  8  days). 

For  intermembranous  bone  select  the  parietal  and  frontal  bones  of  em- 
bryos ;  make  horizontal  sections. 

The  sections  are  to  be  stained  in  4  c.c.  of  Bohmer's  hematoxylin,  2  to  10 
minutes,  transferred  to  10  c.c.  of  distilled  water  for  10  minutes,  then  to  4  c.c. 
of  picrocarmine  for  10  minutes  (pp.  31,  33),  to  20  c.c.  of  distilled  water  for 
from  15  minutes  to  i  hour,  and  mounted  in  damar  (p.  38). 

If  the  staining  is  successful,  the  cartilage  (especially  the  calcified  portions) 
is  blue,  the  bone  red.  Occasionally  the  cartilage  does  not  stain  well ;  then 
place  the  sections  in  5  c.c.  of  distilled  water  plus  5  drops  of  filtered  hema- 
toxylin solution.  In  6  to  14  hours  the  cartilage  will  become  blue.  The  picro- 
carmine staining  of  bone  is  often  not  uniform,  the  youngest  portions  of  the 
bone,  the  margins  of  the  osseous  trabeculse,  for  example,  are  often  the  more 
brilliantly  stained. 

X.   MUSCLES   AND   TENDON. 

No.  62. — Bundles  of  Striped  Afiisele. — Select  a  muscle  in  which  the  fibers 
have  a  parallel  disposition  (for  example,  the  adductor  of  the  rabbit)  and  with 
a  sharp  razor  make  a  deep  incision  transverse  to  the  course  of  the  fibers  and 
2  to  3  cm.  below  a  second  incision  ;  connect  these  by  longitudinal  incisions  and, 
without  traction,  carefully  remove  the  area  thus  mapped  out.  For  fixation 
place  it  in  100  c.c.  of  o.  i  per  cent,  chromic  acid  (p.  27).  After  2  weeks 
wash  it  in  rimning  water  and  harden  in  50  c.c.  of  gradually  strengthened 
alcohol  (p.  29).  Make  cross-sections  and  examine  in  diluted  glycerine  (Fig. 
76).  The  muscle-fibers  vary  greatly  in  thickness  ;  the  smallest  are  sections 
through  the  ends  of  the  fibers.  Although  the  muscle-fibers  are  cylindrical  and 
should  therefore  in  section  appear  circular,  they  have  an  irregularly  polygonal 
outline  due  to  mutual  pressure.  The  color  of  the  sections  is  very  different — 
some  are  quite  dark,  others  quite  clear.  The  cause  of  this  phenomenon  is 
unknown  to  me.  The  endomysium  is  best  seen  with  the  high  power  (240 
diameters) . 

No.  63.  —  Tendons. — Cut  from  a  tendon  a  piece  5  to  10  cm.  long,  and  let  it 
dry  in  the  air  (but  not  in  the  sun).  Thin  tendons  at  room-temperature  are 
sufficiently  dry  in  24  hours.  Thicker  tendons  require  several  days.  With  the 
scalpel  (not  the  razor)  cut  a  smooth  transverse  surface  and  then  cut  thin  shav- 
ings from  the  tendon,  supporting  it  on  the  thumb  of  the  right  hand  and  with 
the  remaining  fingers  grasping  the  scalpel  (the  manipulation  is  the  same  as  in 
sharpening  a  pencil).  Throw  the  majority  of  the  shavings  into  a  capsule  con- 
taining distilled  water,  and  in  2  minutes  examine  in  a  drop  of  the  same  medium 
(Fig.  77,  A).  To  preserve,  stain  in  3  c.c.  of  picrocarmine  for  5  minutes  and 
mount  in   dilute  glycerin,     ^'ery  frequently  a  streak  may  be  seen  extending 


SPECIAL    TF.CHXiyUE.  293 

across  the  entire  section  ;  this  has  been  produced  by  the  knife.  Place  a  second 
section,  unstained,  in  a  drop  of  water  on  a  slide ;  treat  it  under  the  cover- 
glass  with  a  drop  of  acetic  acid  ;  the  edge  of  the  section  soon  exhibits  swollen 
convoluted  bands  (acetic-acid  reaction  of  connective  tissue). 

No.  64. — For  the  study  of  the  minute  structure  of  tendon,  its  cells  and  their 
processes,  place  a  thin  tendon,  as  fresh  as  possible  (that  of  the  ])almans  longus 
muscle)  in  pieces  3  cm.  long  in  100  c.c.  of  0.5  i)er  cent,  cliromic  acid  for  at 
least  4  weeks  ;  the  chromic  acid  should  be  changed  several  times  during  this 
period.  Then  wash  the  tissue  in  running  water,  i  to  2  hours,  and  harden  it  in 
about  40  c.c.  of  gradually  strengthened  alcohol  (p.  29).  The  sections  should 
be  cut  with  a  very  sharp  razor  ;  often  the  tendon  is  so  brittle  that  it  falls  to 
pieces  in  cutting.  The  sections  need  not  be  very  thin.  Mount  them  unstained 
in  diluted  glycerine.  Examined  with  the  low  power  and  reflected  light  (with 
the  mirror  muffled)  they  yield  beautiful  pictures,  better  than  the  preparations 
made  like  Techn.  No.  63.  With  the  high  power  they  resemble  Fig.  77,  B. 
The  black  zigzag  spaces  are  in  part  occupied  by  tendon-cells. 

No.  65. — Tendon-cells. — From  the  tail  of  a  rat  or  mouse  cut  pieces  of 
tendon  0.5  to  i  cm.  long,  and  place  them  in  5  c.c.  of  alum-carmine.  The 
following  day  (or  later)  transfer  the  swollen  pieces  to  a  dry  slide  and  rapidly 
tease  them  (p.  25).  It  is  not  necessary  to  separate  the  tendon  into  very  small 
bundles,  but  care  should  be  taken  that  the  bundles  lie  straight.  Then  cover 
the  preparation  with  a  drop  of  distilled  water  and  a  cover-glass.  With  the 
low  power  the  rows  of  cells  may  be  seen,  appearing  for  the  most  part  as  dark 
streaks  ;  these  are  the  cell-nuclei  seen  in  profile.  In  surface  views  the  nuclei 
appear  dull  red.  The  body  of  the  cells,  the  protoplasm,  can  only  be  seen 
with  the  high  power ;  viewed  laterally,  it  appears  as  a  sharp,  dark  streak,  from 
the  surface,  pale  and  delicate.  Not  infrequently  the  cells  are  folded,  so  that 
they  are  visible  partly  from  the  edge  and  partly  from  the  surface.  The  con- 
nective-tissue fibers  may  be  distinguished  occasionally  as  delicate  parallel  lines  ; 
the  fine  elastic  fibers  with  their  sharp  contours  are  always  distinct.  The  focus 
should  be  changed  by  means  of  the  micrometer-screw,  and  all  the  different 
planes  of  the  section  examined.  If  the  cells  are  not  distinct  add  a  drop  of 
acetic  acid  (p.  41).     To  preserve,  displace  the  water  with  diluted  glycerine. 

No.  66. — Muscle  and  Tendon. — Remove  the  skin  from  the  hind  leg  of  a 
frog  just  killed,  and  with  scissors  cut  off  the  leg  above  the  knee-joint — that  is, 
above  the  origin  of  the  gastrocnemius.  Fix  it  in  50  c.c.  of  Kleinenberg's  picro- 
sulphuric  acid  (p.  28).  After  24  hours  transfer  it  directly  to  50  c.c.  of  70 
per  cent,  alcohol  for  gradual  hardening.  In  about  6  days  cut  off  the  muscle 
with  a  piece  of  the  tendo-Achillis,  and  stain  it  in  bulk  in  borax-carmine 
(p. 32).  Then  harden  again  in  90  jJer  cent,  alcohol.  Cut  sagittal  longitudinal 
sections,  placing  the  razor  on  the  tendon  on  the  posterior  surface  of  the 
muscle.  Mount  in  damar  (p.  38).  Very  often  not  a  trace  of  the  cross- 
striation  of  the  muscle-fibers  is  to  be  seen. 


XI.    rill':  ORGANS  OF  THf-:  NKRVOUS  SYSTEM. 

No.  67.  —  The  Spinal  Cord. — For  the  study  of  the  distribution  of  the 
white  and  gray  substance  the  s|)inal  cord  of  a  child  should  be  fixed  in  toto  in 
about  I  liter  of  Miiller's  fluid,  which  should  be  frequently  changed  ;  after  4 
or  5  months  thick  cross  sections  of  the  cervical,  thoracic,  and  lumbar  regions 
may  be  cut,  and  without  further  treatment  mounted  in  dilute  glycerine  (p.  38), 
or  after  the  customary  preliminary  treatment  they  may  be  mounted  in  damar. 


2  94  HISTOLOGY. 

No.  68.  —  The  Spinal  Cord  ;  Staining  of  Medullaled  Fibers. — The  suc- 
cess of  the  preparation  depends  especially  on  the  state  of  preservation  of  the 
organ.  The  fresher  the  tissue  when  it  is  put  into  the  fixing  fluid,  the  better 
will  be  the  result.  The  entire  spinal  cord  should  be  placed  in  a  large  quantity 
of  Miiller's  fluid,  which  must  be  changed  daily  during  the  first  week  and  fre- 
quently thereafter.  If  it  is  desired  to  investigate  only  portions  of  the  spinal  cord 
then  place  pieces  of  the  fresh  cord  about  2  cm.  long  taken  from  the  lower  cer- 
vical, the  middle  thoracic,  and  the  lumbar  region  in  200  to  500  c.c.  of  Miiller's 
fluid,  or  better,  suspend  them  in  it.  In  4  to  6  weeks,  during  which  time  the  fluid 
must  be  frequently  changed,  the  tissue  is  to  be  transferred  directly,  without 
previous  washing,  to  150  c.c.  of  70  per  cent,  alcohol,  and  on  the  following  day  to 
the  same  quantity  of  90  per  cent,  alcohol.  The  bottle  containing  the  tissue  must 
be  placed  in  the  dark  (p.  29),  and  the  alcohol  frequently  changed  during  the 
first  8  days.  Sections  may  then  be  cut.  The  sections  are  to  be  placed  in  a  cap- 
sule containing  20  c.c.  of  70  per  cent,  alcohol,  and  as  soon  as  possible  trans- 
ferred from  this  to  30  c.c.  of  Weigert's  hematoxylin  to  which  i  c.c.  of  lithium 
carbonate  solution  has  been  added  (p.  22).  In  5  to  6  hours  the  now  very 
dark,  untransparent  sections  should  be  transferred  to  50  c.c.  of  distilled  water 
plus  I  c.c.  of  lithium  carbonate  solution.  In  a  half  hour,  during  which  time 
the  fluid  must  be  changed  several  times,  the  sections  will  give  off  no  more 
color  and  are  then  to  be  placed  in  30  c.c.  of  potassium  permanganate  solution 
for  differentiation.  In  '4  to  3  minutes  the  sections  are  to  be  washed  for  i 
minute  in  distilled  water  and  then  transferred  to  20  c.c.  of  the  acid  mixture. 
The  capsule  containing  the  acid  mixture  should  be  covered.  The  decoloriza- 
tion  occurs  in  10  to  50  seconds;  the  gray  substance  becomes  light  yellow, 
almost  white,  the  white  substance  (the  medullated  nerve-fibers)  very  dark. 
Now  transfer  the  sections  to  a  capsule  containing  30  c.c.  of  distilled  water  and 
in  5  minutes  to  a  second  capsule  containing  the  same  quantity  of  fresh  distilled 
water.  After  10  mintites  place  them  in  10  c.c.  of  alum-carmine,  in  which  they 
may  remain  from  3  to  15  hours.  Mount  in  damar.  The  alum-carmine  staining 
may  be  omitted.  The  foregoing  directions  are  intended  for  thin  well-fixed 
preparations.  If  the  sections  are  thick,  if  the  tissue  has  lain  a  long  time  in  alco- 
hol, more  time  will  be  required  for  staining  and  reduction.  Should  the  sections 
not  stain,  place  them  in  Miiller's  fluid  for  24  hours,  wash  i  minute  in  distilled 
water,  then  stain,  and  the  result  may  be  successful.  Should  the  decolorization 
not  be  sufficient,  if  the  gray  substance  does  not  become  yellowish-white,  the  pro- 
cedure maybe  repeated  ;  that  is,  the  sections  are  to  be  again  placed  in  distilled 
water  i  minute,  then  in  potassium  permanganate  i  to  3  minutes,  then  in  distilled 
water  i  minute,  and  finally  in  the  acid  mixture.  The  given  quantities  of  the 
potassium  solution,  also  of  the  acid  mixture,  are  sufficient  for  only  a  few,  about 
20,  sections.  If  it  is  desired  to  treat  more  sections,  larger  quantities  of  these 
fluids  must  be  used. 

No.  6q. —  The  Spinal  Cord :  S/aining  of  A.xis-cylinders  and  Cells. — Place 
pieces  at  the  most  2  cm.  long  in  200  c.c.  of  Miiller's  fluid,  which  must  be 
changed  daily  during  the  first  week,  and  frequently  thereafter.  In  4  weeks 
transfer  the  tissue  directly  from  the  Miiller's  fluid  to  about  50  c.c.  of  sodium 
carminate  (i  per  cent,  aqueous  solution),  in  which  it  should  remain  for  3 
days.  During  this  time  the  bottle  must  be  frequently  shaken.  The  stained 
pieces  are  to  be  washed  for  24  hours  in  running  water,  then  placed  in  150  c.c. 
of  70  per  cent,  alcohol,  and  after  5  hours  transferred  to  the  same  quantity  of 
96  percent,  alcohol.      Mount  in  damar  (Fig.  86). 

No.  70. — Spinal  Cord ;    Golgi  Staining. — The  length  of  time  the  tissue 


SPF.CIAL    TECHNIQUE.  29S 

must  remain  in  the  Golgi  mixture  depends  upon  the  elements  it  is  desired  to 
stain,  as  follows:  — 

2  to  3  days  for  neuroglia  cells. 

3  to  5  days  for  nerve-cells. 

5  to  7  days  for  nerve-fibers  (collateral  fibrils). 

For  this  purpose  take  the  spinal  cord  with  the  vertebral  column  of  a  new- 
born rat  or  mouse,  and  treat  it  according  to  the  method  given  on  page  35. 
Since  the  pieces  must  be  used  as  soon  as  they  are  taken  out  of  the  silver  solu- 
tion, only  one  piece  at  a  time  should  be  transferred  to  the  absolute  alcohol. 
Cut  the  sections  through  the  cord  and  the  vertebral  column. 

The  spinal  cord  of  a  3-  to  7-days'-old  embryo  chick  furnishes  still  better 
results,  but  it  is  necessary  to  embed  the  tissue  in  celloidin  (see  Microtome 
Technique).     The  spinal  cord  of  kittens  yields  good  results. 

No.  71.  —  The  Brain;  Staining  of  Medullated  Ner-i'e-fibers. — Apply  the 
method  given  in  No.  6S.  If  an  entire  human  brain  is  to  be  placed  in  Miiller's 
fluid,  many  deep  incisions  should  be  made  in  it  and  about  3  liters  of  the  fixing 
fluid  should  be  used. 

No.  72.  —  The  Brain  ;  Cells. — Treat  pieces  i  to  2  cm.  square  of  the  cere- 
bral cortex  (paracentral  convolution)  and  of  the  cerebellar  cortex  like  No.  69. 
In  the  cerebral  cortex,  in  addition  to  the  cell-forms  described,  a  variable  number 
of  vesicular  spaces,  containing  remnants  of  cells 
(protoplasm  and  nuclei),  may  be  seen.     Tliese  .1 

are  probably  pericellular  lymph-spaces,  which, 
by  ])Ost-morteui  alteration  and  the  intluencc  of  ^^ 

the  fixation  medium,  have  become  abnormally  _i. 

enlarged.      The  sections  through  the  cerebellar  ^"^ 

cortex  must  be  made  transverse   to   the  long  fl     & 

axis  of  the  convolution,  since  the  ramifications 
of  the  cells  of  Purkinje  extend  only  in  j)lanes 
transverse  to  the  convolution.      In  the  dejjres-  '''^''1     - 

sions  between  the  convolutions  only  a  few  cells 
of  Purkinje  are  to  be  seen.  Fic.  363.-P0KT10N  op  *  Section  of 

Human   Cfkebral  Cortex.     X   240. 

No.  ^i.-The  Brain:  Golgi  Staining.-  ^•.c'cTsfora'pJrfJidSl'Uu'''''''  """" 
a.    I' or  a  general  view,  treat   the  brain  of  a 

newborn  rat  or  mouse  in  the  unopened  cranium  according  to  the  method  given 
in  No.  70.     The  cranium  may  be  sectioned  with  the  brain-substance. 

l>.  F"or  specimens  of  the  cortex,  treat  pieces  of  the  brain  of  an  8-  to  30- 
days'-old  mouse  with  the  Golgi  mixture  for  from  2  to  3  days,  or  of  a  i-  to  15- 
days'-old  rabbit,  or  a  kitten  under  6  weeks  old,  for  5  days.  Pieces  of  the 
brain  of  adults  must  remain  in  the  Golgi  mixture  S  to  15  days.  Further  treat- 
ment like  No.  70. 

No.  74. — The  Cortex  0/  the  CereMli/m  ;  Golgi  Staining. — Remove  the 
cerebellum  from  the  cranium  of  a  newborn  guinea-pig  (or  a  kitten  less  than 
6  weeks  old)  and  treat  it  according  to  the  method  given  in  No.  70.  The 
staining  of  the  elements  of  the  cerebellum  is  more  difficult  to  accomplish  than 
of  the  cerebrum  and  the  spinal  cord.  Failures  are  frequent.  The  sections 
shotild  he  princijwlly  made  vertically  to  the  axis  of  the  convolutions.  (For 
embedding,  see  Microtome  Technique.) 

-^'^-    75- — Hypophysis  Cerebri. — Treat  like  No.  80. 

No.    76. — Brain-sand,  AeerTiiliis  Cerebri. — Tease  the  epiphysis  in  a  drop 


296  HISTOLOGY. 

of  salt  solution.  If  much  brain-sand  is  present,  a  gritty  sound  will  be  heard  on 
teasing  and  the  larger  concretions  can  be  perceived  by  the  unaided'  eye.  Ex- 
amine with  the  low  power,  without  a  cover-glass  (Fig.  99).  Often  the 
irregularity  of  the  surface  is  indistinct.  Push  aside  the  larger  granules  with 
a  needle,  cover  a  few  of  the  smaller  ones  with  a  cover-glass  and  treat  with  2  to 
3  drops  of  hydrochloric  acid  (p.  20).  Bubbles  of  gas  develop  and  the  sharp 
outlines  of  the  granules  disappear. 

No.  11.— Corpora  Amylacea. — Select  the  brains  of  elderly  individuals. 
With  a  scalpel  scrape  the  mesial  surface  of  the  optic  thalamus — that  directed 
toward  the  third  ventricle — and  spread  the  scrapings  with  a  needle  in  a  drop 
of  salt  solution  ;  apply  a  cover-glass.  The  corpuscles  when  present  are  easily 
found,  and  are  recognized  by  their  bluish-green  color  and  their  stratification 
(Fig.  100,  a).  They  should  not  be  confused  with  drops  of  extruded  myelin 
(/'),  which  are  always  clear  and  have  a  double  contour.  In  addition  there  may 
be  found  in  such  preparations  numerous  red  blood-corpuscles,  ependymal  cells 
(;/),  medullated  nerve-fibers  varying  in  thickness,  and  ganglion-cells;  the 
latter  are  very  pale  and  often  can  only  be  detected  by  their  pigmentation  (y). 
Human  brains,  even  though  not  absolutely  fresh,  can  still  be  used. 


^       J 


ERiPHERAL  (Spinal)  Nbrve  OF  Rabp.it.  X  50.  In  the 
srse  sections  of  nerve-fibers  have  fallen  out.  others  are  lying 
endoneurium  is  but  slightly  developed  in  the  rabbit. 

No.  78. — Spread  out  a  piece  i  cm.  long  of  the  choroid  plexus  in  a  drop 
of  salt  solution  and  apply  a  cover-glass.  The  convoluted  red  blood-vessels  and 
the  epithelium  of  the  plexus  can  be  seen. 

No.  79. — Transverse  Sections  of  Neroe-Ji/'er  Bundles. — Treat  a  piece  of 
nerve,  if  possible  the  sciatic  of  man,  which  possesses  a  well-developed  endo- 
neurium, according  to  the  method  given  in  No.  30.  Place  it  for  6  days  in  a 
0.1  per  cent,  solution  of  chromic  acid,  then  wash  it  for  from  3  to  4  hours  in 
running  water,  and  harden  it  in  gradually  strengthened  alcohol.  When  the 
hardening  is  completed,  cut  thin  sections  with  a  sharp  razor.  It  is  advisable  to 
embed  the  tissue  in  liver  ;  better  still,  in  elder  pith,  or  in  the  pith  of  the  sun- 
flower. For  this  purpose,  make  a  hole  in  the  dry  elder  jiith  with  a  needle,  and 
then  carefully  insert  the  nerve.  Place  the  whole  for  about  a  half-hour  in  water  ; 
the  pith  swells  and  firmly  grasps  the  nerve.  Stain  the  sections  in  picrocar- 
mine,  and  mount  in  glycerine.  The  length  of  time  required  for  staining  varies 
greatly.     The  sections  must  be  very  carefully  handled  and  pressure  with  the 


SPECIAL   TECHNIQUE.  297 

cover-glass  must  be  scrupulously  avoided,  lest  the  sections  of  the  fibers,  which 
are  not  disks  but  short  cylinders,  be  turned  on  their  sides,  and  not  a  fiber  in 
section  be  seen.  If  successful,  the  section  will  show  a  somewhat  shrunken 
axis-cylinder,  resembling  a  red  nucleus,  surrounded  by  the  yellow  medulla, 
enclosed  by  the  reddish  neurilemma.  The  cross-section  of  the  nerve-fiber  has 
been  compared  to  a  picture  of  the  sun  {SonnenbilJchenfigidr)  (Fig.  102  j. 

No.  80. — Spinal  Ganglia. — These  are  difficult  to  obtain.  Therefore  re- 
move the  Gasserian  ganglion  from  the  depression  in  which  it  is  lodged  (on  the 
anterior  surface  of  the  ])etrous  jwrtion  of  the  temjjoral  boiiej,  and  place  it  in 
about  100  c.c.  of  Miiller's  fluid  for  fixation.  .After  4  weeks  wash  it  for  3 
hours  in  running  water,  and  harden  it  in  50  c.c.  of  gradually  strengthened 
alcohol  (p.  29).  Cut  the  thinnest  possible  transverse  and  longitudinal  sec- 
tions ;  stain  them  30  seconds  in  hematoxylin,  and  then  2  to  5  minutes  in  eosin 
(]).  32,  3  F),  and  mount  in  damar.  The  ganglion-cells  are  pale  red  ;  the  axis- 
cylinder  deep  red  :  the  medullary  sheath  brownish  ;  the  nuclei  blue  (  Fig.  103). 
If  the  section  is  not  sufficiently  thin,  the  large  number  of  deeply-stained  nuclei 
will  render  it  difficult  to  see  the  other  stnictures.  For  this  reason  it  is  better 
to  stain  thick  sections  in  picrocarmine,  2  to  3  days,  and  mount  them  in  damar. 
The  nuclei  are  then  not  so  intensely  stained.  Occasionally  the  protoplasm  of 
the  ganglion-cell  contracts,  and  thus  acquires  a  stellate  outline  (Pig.  103  x), 
which  the  beginner  may  easily  confiise  with  a  multipolar  ganglion-cell.  Fixa- 
tion in  Kleinenberg's  picrosulphuric  acid  gives  very  good  results. 

T-shaped  branches  may  be  seen  in  preparations  of  thes|)inal  cord  treated  as 
in  No.  70.  In  young  embryo  chicks  the  s|)inal  ganglion-cells  are  still  bipolar. 
Unipolar  cells  are  found  in  embryo  chicks  about  i  7  days  old  ;  transition  forms 
between  the  9th  and  14th  days,  and  in  embryo  rabbits  5  to  12  cm.  long. 

Xo.  81. — Sympathetic  Ganj^/ia. — Fix  and  harden  the  large  superior  cervi- 
cal ganglion  of  the  sympathetic  nerve  like  Xo.  80.  Here,  too,  on  account  of 
the  abundance  of  nuclei,  nuclear  staining  is  ap]jlicable  only  to  very  thin  sec- 
tions. Treated  according  to  the  method  given  in  Xo.  80,  the  processes  of  the 
multijiolar  ganglion-cells  are  not  rendered  distinct.  For  this  purpose  place 
the  thinnest  jjossible  sections  for  24  hours  in  5  c.c.  of  nigrosin  solution  (pre- 
pared like  the  methyl-violet  solution,  p.  23  )  ;  then  transfer  them  to  5  c.c.  of 
absolute  alcohol  for  5  minutes,  and  preserve  in  damar.  The  characteristic 
bundles  of  nonmedullated  nerve-fibers,  cut  oblicjuely  and  transversely,  can  be 
recognized  with  the  low  power;  also  the  ganglion-cells;  but  to  see  their  pro- 
cesses high  magnification  and  careful  scrutiny  are  necessary.  In  many  sec- 
tions the  ])roce.sses  of  the  ganglion-cells  cannot  be  seen  ;  the  latter  may  be  best 
exhibited  according  to  the  method  given  in  No.  70,  and  a  suitable  object  is  the 
cervical  portion  of  a  10-  to  i5-days'-old  embryo  chick. 

No.  82. — Simple  Tactile-cells;  Intra-epitlielial  Nei~'e-fibers ;  Cells  of 
Langerhans ;  Tactile  Corpuscles. — Prepare  a  mixture  of  gold  chloride  and 
formic  acid  ('p.  37),  boil  it  and  let  it  cool  ;  then  cut  from  the  volar 
side  of  a  freshly-amputated  finger  or  toe  (with  scissors  a])piied  flatwise) 
several  small  |)ieces  of  the  e])idermis  and  uppermost  layers  of  the  corium, 
about  5  mm.  long  and  i  mm.  broad.  Carefully  remove  any  fat  attached  to 
the  under  surface  of  the  corium  and  place  the  |)ieces  in  the  gold  and  formic 
acid  mixture  for  i  hour,  ///  the  dark.  Then,  with  glass  rods,  transfer  the 
pieces  to  10  c.c.  of  distilled  water  and  in  a  few  minutes  to  fresh  distilled  water 
to  which  formic  acid  has  been  added,  and  expose  the  whole  to  daylight  (sun- 
light is  unnecessary).     In    24  to  48  hours  the  tissue  becomes  dark  violet.     It 


290  HISTOLOGY. 

is  now  to  be  hardened  in  30  c.c.  of  gradually  strengthened  alcohol.  In  8  days  the 
pieces  may  be  embedded  in  liver  and  sectioned  ;  mount  in  damar.  The  epi- 
dermis is  red-violet  in  different  tints ;  the  nuclei  are  only  to  be  seen  in  places 
and  often  are  not  perceptible  ;  the  corium  is  white  ;  the  capillaries,  the  excre- 
tory ducts  of  the  coil-glands,  and  the  nerves  are  dark  violet  to  black.  For 
tactile-cells  the  thinnest  possible  sections  are  necessary.  They  may  often  be 
found  near  the  excretory  ducts  of  the  coil-glands.  Care  must  be  taken  not  to 
confuse  them  with  shrunken  epithelial  cells  (Fig.  106). 

The  intra-cpltlielial  nerve-fibers  appear  as  delicate  filaments  ;  their  connec- 
tion with  the  nerve-fibers  in  the  corium  is  difficult  to  trace.  Processes  of  the 
cells  of  Langerhans,  in  thin  sections,  are  apt  to  be  confused  with  the  intra- 
epithelial nerve-fibers  (Fig.  105). 

The  cells  of  Langerhans  and  the  tactile  corpuscles  may  be  easily  seen  ;  in 
thick  sections  the  tactile  corpuscles  are  black  (Fig.  105),  in  thin  sections  red- 
violet  (Fig.  no). 

No.  83.  —  Compound  Tactile-cells. — Cut  the  yellowish  wax-like  skin,  or 
cere,  from  the  lateral  edges  of  the  upper  beak  of  a  duck  or  goose  and  treat 
pieces  i  to  2  mm.  thick  and  i  cm.  long  with  3  c.c.  of  2  per  cent,  osmic-acid 
solution  plus  3  c.c.  of  distilled  water;  place  the  whole  in  the  dark  18  to  24 
hours  ;  then  wash  the  pieces  for  i  hour  in  running  water  and  transfer  them  to  20 
c.c.  of  90  per  cent,  alcohol.  In  6  hours  the  objects  maybe  sectioned.  Embed 
them  in  liver  and  make  the  sections  from  the  corium  toward  the  epithelium,  not 
the  reverse.  The  sections  may  be  mounted  unstained  in  damar.  The  olive- 
green  tactile-cells  may  be  readily  seen,  but  the  entrance  of  the  nerve- fiber  is 
difficult  to  find  (Fig.  107).  In  addition,  Herbst's  corpuscles  occur  in  the 
sections.  If  it  is  desired  to  stain  the  sections,  use  a  nuclear  staining  solution 
(P-  31)- 

No.  84. — Cylindrical  End-bulbs. — ^With  scissors  and  forceps  cut  out  pieces 
I  cm.  square  of  the  scleral  conjunctiva  near  the  corneal  margin  of  the  fresh 
eye  of  a  calf,  taking  care  not  to  roll  them.  It  is  better  to  let  them  lie  smooth 
on  the  sclera.  Carefully  slip  the  pieces,  epithelial  side  up,  from  the  sclera 
on  to  a  cork-plate,  and  span  them  out  with  needles.  Moisten  the  surface  with 
a  {i\i  drops  of  the  vitreous  humor  obtained  from  the  eye  ;  with  scissors  and 
forceps  dissect  off  a  thin  layer  consisting  of  connective  tissue  and  the  epithelium 
resting  upon  it.  This  operation  must  be  done  with  great  care  ;  folding  and 
torsion  of  the  membrane  must  as  far  as  possible  be  avoided.  The  pieces,  with 
the  epithelial  side  up,  should  now  be  slipped  on  to  a  dry  slide  and  spread  out 
flat.  At  first  they  draw  together,  but  in  a  moment  or  two  the  edges  dry  some- 
what and  adhere  to  the  glass,  and  they  can  then  be  extended  without  much  dif- 
ficulty. The  slide  with  the  preparation  is  next  to  be  placed  in  a  glass  jar  contain- 
ing 65  c.c.  of  distilled  water  to  which  2  c.c.  of  acetic  acid  have  been  added. 
In  about  an  hour  (or  later),  during  which  time  the  pieces  swell  considerably 
and  float  from  the  slide,  with  a  clean  needle  endeavor  to  remove  the  epithe- 
lium ;  it  may  be  loosened  without  much  trouble  and  floats  off  in  fine  white  shreds. 
If  this  is  not  done  cautiously  the  end-bulbs  lying  close  beneath  the  epithelium 
mav  be  torn  off  with  it.  After  the  pieces  have  lain  4  to  5  hours  in  dilute  acetic 
acid  transfer  them  with  a  few  drops  of  the  same  fluid  to  a  slide,  apply  a  cover- 
glass  and  make  slight  pressure  upon  it  with  the  outspread  branches  of  the  forceps. 
On  examination  with  the  low  power  the  blood-vessels  may  be  distinctly  seen — 
they  may  be  recognized  by  their  prominent  nuclei — and  also  the  medullated 
nerve-fibers.  Trace  such  a  fiber  until  the  medulla  ceases  ;  examine  such  places 
with  the  high  power,  for  there  the  end-bulbs  are  most  apt  to  be  found.      In  most 


SPECIAL    TF.CHNIQUE.  299 

cases  nothing  will  be  seen  but  the  numerous  nuclei,  and  even  when  a  favorable 
situation  is  found  the  end-bulbs  are  so  pale  that  it  is  very  difficult  to  perceive 
them  ;  the  axis-cylinder,  too,  is  often  very  difficult  to  see.  Only  the  practised 
microscopist  will  have  much  success  in  finding  them.  Beginners  are  advised 
not  to  attempt  this  jireparation. 

Xo.  85. — Corpuscles  of  Valcr. — These  are  best  obtained  from  the  mes- 
entery of  a  cat,  where  they  may  be  seen  with  the  unaided  eye.  They  appear 
as  milky,  glass-like,  transparent  oval  spots  between  the  strands  of  adipose 
tis.sue  of  the  mesentery.  Their  number  varies  greatly.  Occasionally  they  are 
very  scarce  and  of  such  small  size  that  to  find  them  requires  close  searching. 
Cut  out  the  portion  of  the  mesentery  containing  the  corpuscles,  and  spread 
them  out  in  a  drop  of  salt  solution  on  a  slide  lying  on  a  black  background. 
Endeavor  to  remove  the  attached  clusters  of  fat-cells,  taking  care  not  to  prick 
the  corpuscles.  Ascertain  with  a  low  power,  without  a  cover-glass,  whether  the 
corpuscles  have  been  sufficiently  isolated.  Cover  them  with  another  drop  of 
.salt  solution  and  a  cover-gla.ss.  Pressure  must  be  carefully  avoided.  The 
corpuscle  rejiresented  in  Fig.  109  was  of  very  small  size.  With  the  high  power 
one  can  distinctly  see  the  nuclei  of  the  cells  lining  the  capsules  ;  on  the  other 
hand,  the  oval  nuclei  of  the  inner  bulb  are  often  indistinct  and  pale.  If  it  is 
desired  to  ]>reserve  the  preparation,  treat  it  under  the  cover-glass  with  i  to  2  drops 
of  I  per  cent,  osmic  acid  and,  after  the  medulla  is  blackened  and  the  inner- 
bulb  has  become  brown,  displace  the  acid  with  very  dilute  glycerine.  Methylene- 
blue  staining  (p.  34)  is  recommended. 

No.  86. — Afotor  Nen'c-cniii>i};s — a.  Terminal  Ramifications. — Prepare  a 
mi.vture  of  24  c.c.  of  i  per  cent,  gold  chloride  solution  plus  6  c.c.  of  formic 
acid,  boil  it  and  let  it  cool  ;  cut  out  small  pieces,  3  to  4  cm.  long,  of  the 
intercostal  muscles  of  a  rabbit,  and  treat  them  like  No.  82  ;  after  the 
dark-violet  pieces  have  lain  3  to  6  days  in  70  per  cent,  alcohol,  tease  a 
muscle-bundle  about  5  mm.  broad  in  a  drop  of  dilute  glycerine  to  which  a  very 
small  drop  of  formic  acid  has  been  added.  It  is  of  advantage  to  make  slight 
pressure  on  the  cover-glass.  To  find  the  terminal  ramifications,  trace  with  the 
low  power  the  easily  recognized  black  nerve-fibers  (Fig.  1 1 1 ).  The  addition  of 
another  drop  of  acetic  or  formic  acid  often  renders  the  elements  more  distinct. 

h.  iViielei  of  the.  Motor-plates. — Place  the  anterior  halves  of  the  eye-muscles 
of  a  recently-killed  rabbit  in  97  c.c.  of  distilled  water  plus  3  c.c.  of  acetic 
acid.  After  6  hours  transfer  the  muscles  to  distilled  water ;  with  the  scissors 
cut  a  thin  flat  piece  and  spread  it  out  on  a  slide;  the  ramifications  of  the 
whitish  nerves  can  be  plainly  seen  with  the  unaided  eye.  With  low  magnifica- 
tion (50  diameters),  the  anastomoses  of  the  nerve-bundles,  as  well  as  the 
blood-vessels  (easily  recognized  by  the  transversely-jjlaced  nuclei  of  their 
smooth  muscle-fibers)  can  be  seen.  On  account  of  the  large  number  of 
sharplv-contoured  nuclei  belonging  to  the  muscles  and  the  intramuscular  con- 
nective tissue,  the  end-plates  are  not  easy  to  find.  If  a  nerve-fiber  be  traced 
it  will  soon  be  seen  that  the  double-contoured  medullary-sheath  cea.ses  abruptly 
and  loses  itself  in  a  grouj)  of  nuclei  ;  these  are  the  nuclei  of  the  motor-plate, 
whose  other  details  are  not  distinctly  visible.  The  cross-striation  of  the  muscle- 
fibers,  which  are  very  pale,  is  often  indistinct  (Fig.  112). 

Xo.  87.  —  The  Suprarenal  Bodies  ;  General  Vie70. — Fi.K  the  entire  su|jra- 
renal  body  of  a  child  in  200  c.c.  of  o.i  per  cent,  chromic  acid,  and  after  8 
days  harden  it  in  150  c.c.  of  gradually  strengthened  alcohol  ;  mount  unstained 
sections  in  dilute  glycerine  (Fig.  113  A\ 


300  HISTOLOGY. 

No.  88. — Elements  of  the  Suprareiiat  Body. — Tease  portions  of  the 
fresh  organ  in  a  drop  of  salt  solution.  The  elements  are  very  delicate  and  in- 
jured cells  are  therefore  of  frequent  occurrence. 

No.  89. — For  the  study  of  the  minute  structure  of  the  suprarenal  bodies, 
place  2  cm.  cubes  of  the  fresh  organs  in  100  c.c.  of  Kleinenberg's  picrosul- 
phuric  acid,  and  after  12  to  24  hours  in  an  equal  quantity  of  gradually 
strengthened  alcohol  ;  cut  fine  sections,  stain  them  in  Bohmer's  hematoxylin 
and  mount  in  damar  (Fig.  113  B). 


XII.  THE    DIGESTIVE    TRACT. 

No.  90. — Isolated  Squamous  Cells  from  the  Oral  Cavity. — -With  a  scalpel 
gently  scrape  the  upper  surface  of  the  tongue  and  mix  the  scrapings  with  a  drop 
of  salt  solution  on  a  slide  ;  apply  a  cover-glass  ;  in  addition  to  isolated,  pale, 
squamous  epithelial  cells,  leucocytes  ("  salivary  corpuscles  ")  maybe  found; 
also,  with  more  vigorous  scraping,  the  torn  apices  of  filiform  papillae,  which 
not  infrequently  are  surrounded  by  finely  granular,  dark  masses  of  micrococci 
to  which  tufts  of  leptothrix  buccalis  are  attached.  The  preparation  may  be 
stained  under  the  cover-glass  with  picrocarmine  and  then  treated  with  dilute 
acidulated  glycerine,  provided  too  many  air-bubbles  do  not  make  the  preserva- 
tion of  the  preparation  impossible  (Fig.  6,  i). 

No.  91. — Mucous  Glands  of  the  Lips. — These  are  millet-sized  nodules 
macroscopically  perceptible  to  touch  and  sight.  For  microscopic  preparations 
cut  from  the  mucous  membrane  of  a  human  lower  lip  (not  the  margin  of  the 
lip)  I  cm.  cubes;  fix  them  in  50  c.c.  of  Kleinenberg's  picrosulphuric  acid  and 
in  24  hours  harden  in  50  c.c.  of  gradually  strengthened  alcohol.  In  3  days 
the  tissue  may  be  sectioned.  C\it  many  sections,  not  too  thin,  and  stain  them 
with  Bohmer's  hematoxylin  ;  place  the  sections  in  water,  and  with  the  naked 
eye  select  those  which  include  the  excretory  duct  and  preserve  them  in  damar ; 
examine  with  a  low  power  (Fig.  114). 

No.  92. — Dried  Tooth. — To  prepare  dried  ground  sections  of  teeth  they 
should  be  obtained  immediately  after  they  are  extracted,  sawed  into  transverse 
disks  2  mm.  thick,  and  glued  with  sealing-wax  upon  cork  and  treated  like  No. 
55.  If  longitudinal  sections  are  desired  the  entire  tooth  should  be  glued  to 
the  cork.  Longitudinal  sections  are  to  be  i)referred,  since  thev  show  all  parts 
of  the  tooth  in  a  single  preparation.  If  it  is  desired  to  decalcify  the  teeth  of 
an  adult,  treat  like  No.  57.  The  enamel  contains  only  3  to  5  per  cent,  of 
organic  substances  and  dissolves  completely,  so  that  only  the  dentine  and 
cementum  remain  (Fig.  115,  116,  117). 

No.  93. — Odontoblasts. — Remove  the  teeth  from  the  jaws  of  a  newborn 
child  ;  place  them  in  60  c.c.  of  Miiller's  fluid  ;  after  6  days  the  pulp  can  be 
easily  withdrawn  in  toto  by  means  of  forceps.  With  the  scissors  cut  from  the 
upper  surface  of  the  pulp  a  piece  the  size  of  a  lentil,  and  tease  it  a  little  in  a 
drop  of  Miiller's  fluid  ;  it  is  moderately  tenacious;  apply  a  cover-glass,  press 
lightly  upon  it,  and  examine  with  the  high  power.  At  the  edges  of  the  pre- 
paration the  long  processes  of  the  odontoblasts  will  be  seen  ;  also  scattered 
completely  isolated  odontoblasts  (Fig.  119).  In  order  to  preserve,  treat  under 
the  cover-glass  with  distilled  water  for  2  minutes,  then  with  picrocarmine  ; 
when  the  staining  is  completed,  add  dilute  acidulated  glycerine. 

No.  94. — Enamel  Prisms. — These  may  be  obtained  by  teasing  portions  of 
the  lateral  surface  of  the  teeth  of  No.  93  in  a  drop  of  Miiller's  fluid.      Examine 


SPECIAL   TECHXIQUK.  30I 

with  a  high  power.  The  enamel  prisms  will  be  found  in  groups  of  3  and  4  and  are 
distinguished  by  their  dark  outlines  and  usually  indistinct  cross-striation  (Fig. 
ii8j.  Mount  in  glycerine.  The  prismatic  form  of  the  enamel  i)risms  may  be 
seen  in  thin  sections  cut  parallel  to  the  surface  of  the  teeth.  Only  portions  of 
a  section  exhibit  regular  hexagonal  prisms,  that  is,  cross-sections  of  the  prisms 
(Fig.  118).  The  enamel  of  younger  teeth  may  be  sectioned  without  previous 
decalcification. 

No.  95. — Development  of  Teeth. — For  the  study  of  the  early  stages  select 
pig  and  shee[)  embryos  ;  these  are  the  most  easily  obtained  at  the  slaughter 
houses  ;  for  the  first  stages  the  pig  embryos  should  have  a  size  of  about  6  cm., 
for  the  second  stage  a  size  of  about  10  to  11  cm.  For  later  stages  the  inferior 
maxilla  of  newborn  dogs  or  cats  are  very  suitable.  Place  the  heads  (or  the 
lower  jaws)  in  100  c.c.  of  Kleinenberg's  picrosulphuric  acid,  12  to  24  hours, 
and  harden  in  80  to  120  c.c.  of  gradually  strengthened  alcohol.  After  the 
heads  have  lain  6  to  8  days  in  90  per  cent,  alcohol,  they  are  to  be  decalcified 
in  100  c.c.  of  distilled  water  plus  i  or  2  c.c.  of  nitric  acid.  When  the  de- 
calcification is  completed,  in  3  to  8  days,  harden  again  in  alcohol.  In  5  to  6 
days  cut  off  the  lower  jaw  and  divide  it  in  front  in  the  middle  (larger  jaws 
should  be  cut  vertically  into  pieces  i  to  2  cm.  long)  ;  stain  the  pieces  in  bulk 
in  borax-carmine.  When  the  staining  and  decolorization  are  completed,  the 
tissue  is  to  be  transferred  to  absolute  alcohol,  in  which  it  must  remain  for  sev- 
eral days  ;  it  is  then  to  be  embedded  in  liver  and  sectioned.  It  is  necessary  to 
cut  many  (20  to  40)  thick  sections,  since  only  those  which  pass  through  the 
middle  of  the  tooth,  or  the  anlage  of  the  tooth,  can  be  used.  Blount  in  damar. 
Not  infrequently  in  sectioning  the  enamel  organ  separates  from  the  papilla,  so 
that  a  free  space  exists  between  the  two.  The  dentine  is  often  stained  in  dif- 
ferent tones  of  red  ;  this  is  due  to  the  different  ages  of  the  calcified  and  uncal- 
cified  strata  of  the  dentine.  The  objects  may  also  be  fixed  in  Miiller's  fluid  ; 
section-staining  in  hematoxylin  is  not  advisable,  since  too  many  sections  must 
be  stained  which  on  investigation  are  found  to  be  useless. 

No.  96. — Papill(Z  Fillformes,  Fiingiformes,  Circiimvallata: ;  Follicles  of  the 
Tongue. — Cut  pieces  2  cm.  square  from  the  mucous  membrane  of  the  surface 
of  a  human  tongue.  Each  piece  should  have  some  of  the  muscle  tissue  at- 
tached to  its  lower  surface;  for  fungiform  papillte  cut  the  piece  from  the  tip  of 
the  tongue;  for  filiform,  from  the  middle  of  the  dorsum  of  the  tongue;  for 
circumvallate,  from  the  root  of  the  tongue,  and  for  follicles  (the  puncti- 
form  openings  of  which  can  be  seen  with  the  naked  eye)  from  the  root  of 
the  tongue,  and  place  them  in  100  to  200  c.c.  of  Miiller's  fluid.  The  fluid 
must  be  changed  several  times  ;  after  2  weeks  wash  the  tissue  and  harden  it  in 
50  c.c.  of  gradually  strengthened  alcohol.  For  filiform  papillce  cut  thick  sag- 
gital  sections  of  the  tongue  and  do  not  stain  them  ;  stain  the  other  sections  in 
Bohmer's  hematoxylin  and  mount  in  damar  (Fig.  125,  126,  127).  For  the 
preparations  represented  in  Fig.  12S  and  Fig.  130  the  tissue  was  fixed  and 
hardened  in  50  c.c.  of  absolute  alcohol.  Rabbits'  tongues  may  be  placed  in 
toto  in  200  c.c.  of  Miiller's  fluid;  the  subsequent  treatment  is  the  same. 
Thick  cross-sections  through  the  anterior  half  of  the  entire  tongue  are  suitable 
for  the  study  of  the  arrangement  of  the  muscles  of  the  tongue.  Thin  sections 
of  the  root  of  the  tongue  show  beautiful  mucous  and  serous  glands. 

No.  97.  —  The  Tonsils. — The  tonsils  of  adult  man  do  not  furnish  instruc- 
tive preparations.  They  should  be  treated  like  No.  96.  The  tonsils  of  the 
rabbit  and  the  cat  are  to  be  recommended  ;  to  find  these  proceed  as  follows : — 

Dissect    the   skin    from    the   anterior   surface  of  the    neck    and    remove 


302  HISTOLOGY. 

the  structures  lying  over  the  trachea  and  esophagus ;  with  a  pair  of  stout 
scissors  cut  through  both  tubes  above  the  sternum,  grasp  the  cut  ends  with  for- 
ceps, and  with  scissors  dissect  them  up  to  the  head  of  the  pharynx,  keeping 
close  to  the  anterior  surface  of  the  vertebral  column  (at  the  same  time  the 
cornua  of  the  hyoid  bone  will  be  divided).  Cut  through  the  musculature  close 
to  the  median  edges  of  the  inferior  maxilla,  and  also  through  the  ligaments  of 
the  tongue  (glosso-epiglottic).  (In  the  rabbit  it  is  advisable  to  divide  both 
angles  of  the  mouth,  and  with  scissors  introduced  within  the  slit  to  sever 
the  ligaments  and  the  genio-hyoglossus  muscle.)  Draw  the  trachea  and 
attached  structures  downward,  press  the  tongue  down  between  the  rami  of  the 
inferior  maxilla,  and  divide  its  remaining  attachments  (to  the  palate)  close  to 
the  bone.  Put  the  tongue  down  with  its  free  surface  looking  upward.  With 
delicate  scissors  divide  the  posterior  wall  of  the  pharynx  in  the  median  line 
down  to  the  larynx  and  pull  the  walls  apart ;  the  tonsils  will  then  be  seen  as  a 
pair  of  oval  prominences,  about  5  mm.  long,  on  the  lateral  walls  of  the  phar- 
ynx. They  may  be  fixed  in  60  c.c.  of  Kleinenberg's  picrosulphuric  acid 
(p. 28),  and  hardened  in  50  c.c.  of  gradually  strengthened  alcohols  (p.  29), 
stained  with  hematoxylin  or  with  eosin  and  hematoxylin  (p.  31),  and  mounted 
in  damar. 

No.  98.  —  The  Esophagus. — Pieces  of  human  esophagus  2  cm.  square  and 
of  that  of  the  rabbit  and  cat  2  cm.  long  of  the  entire  tube  are  to  be  fixed  in 
60  c.c.  of  Miiller's  fluid  and  in  2  weeks  hardened  in  50  c.c.  of  gradually 
strengthened  alcohol;  stain  with  Bohmer's  hematoxylin;  mount  in  damar 
(Fig.  131). 

No.  99.  —  The  Mucous  Membrane  of  the  Stomach. — For  topographical 
preparations  place  pieces  2  to  5  cm.  square  for  6  hours  in  100  c.c.  of  3  per 
cent,  nitric  acid.  Remove  the  gastric  contents  adhering  to  the  mucous 
membrane  by  moving  it  slowly  to  and  fro  in  the  acid.  In  a  half  hour  renew 
the  acid,  and  harden  in  60  c.c.  of  gradually  strengthened  alcohol.  Mount 
thick  unstained  sections  in  damar  (Fig.  132). 

No.  100. — Fresh  Gastric  Glands. — From  the  fundus  of  the  stomach  of  a 
rabbit  just  killed  cut  pieces  about  2  cm.  square  and  separate  the  loosely- 
attached  muscular  coat  from  the  mucous  membrane.  Grasp  the  latter  with  for- 
ceps at  the  left  edge  and  with  fine  scissors  cut  very  thin  strips,  0.5  to  1  mm. 
thick;  tease  them  in  a  drop  of  0.5  salt  solution.  The  body  and  fundus  of 
the  fundus  glands  can  be  satisfactorily  isolated  without  much  trouble.  The 
bodies  of  the  parietal-cells  may  be  distinctly  seen  (Fig.  265,  B),  the  chief-cells 
are  not  visible.  The  nuclei  may  be  stained  with  picrocarmine  and  the  prepa- 
ration mounted  in  dilute  glycerine.  The  isolation  of  the  pylorus  glands  can 
only  be  accomplished  by  very  careful  teasing. 

No.  loi. — Isolated  Gastric  Epithelium. — Place  pieces  i  cm.  square  of 
gastric  mucous  membrane  for  about  5  hours  in  30  c.c.  of  Ranvier's  alcohol 
(see  further  p.  26  a).  In  the  majority  of  the  cells  the  mucous  portion  occupies 
a  large  division,  and  they  have  the  appearance  of  those  pictured  in  Fig.  -12  c. 
The  preparation  may  be  stained  under  the  cover-glass  with  picrocarmine,  and 
mounted  in  diluted  acidulated  glycerine. 

No.  102. — Gastric  Glands. — -The  stomach  of  a  cat  or  dog  that  if  possi- 
ble has  been  fasting  for  one  or  two  days  is  especially  to  be  recommended.  The 
stomach  of  the  rabbit,  on  account  of  the  very  small  size  of  the  chief-cells,  is 
less  suitable.  Dissect  off  the  mucous  membrane  from  the  muscular  coat  and 
place  pieces  of  the  former  about   i  cm.  square   in   about  10  c.c.  of  absolute 


SPECIAL   TECHNIQUE.  303 

alcohol.  In  about  a  half-hour  transfer  them  to  20  c.c.  of  fresh  alcohol.  The 
outlines  of  the  glands  can  be  recognized  in  moderately  thin  sections ;  the  only 
difficulty  is  the  circumstance  that  the  gland-tubules  are  placed  very  close 
together.  The  beginner  may  not  recognize  the  glands  and  may  mistake  for 
them  the  gastric  pits  lined  with  clear  epithelium.  The  stomach  of  man,  which 
however  is  suitable  for  use  only  for  a  few  hours  after  death,  exhibits  this  diffi- 
culty in  a  less  degree.  For  the  study  of  the  minute  structure  of  the  glands  and 
of  the  superficial  eijithelium,  embed  the  tissue  in  liver  and  cut  the  thinnest  pos- 
sible sections. 

a.  For  fundus  glands,  chief-  and  parit-tal-cflls,  cut  vertical  or  better  hori- 
zontal sections  of  the  mucous  membrane  and  stain  them  with  Bohmer's  hema- 
toxylin, 2  to  4  minutes.  Wash  the  sections  thoroughly  in  30  c.c.  of  distilled 
water,  which  must  be  changed  as  often  as  it  becomes  bluish — about  once  or 
twice.  Transfer  them  to  5  c.c.  of  a  ^^  per  cent,  solution  of  Congo  red  (p. 
23),  3  to  6  minutes,  wash  2  minutes  in  distilled  water,  and  mount  in  damar. 
If  the  sections  are  too  thick,  everything  appears  red;  the  large  red  parietal- 
cells  cover  the  smaller  chief-cells  ;  e.xamine  the  thinnest 

parts  of  the  sections,  especially  the  fundi  of  the  glands, 
where  the  parietal-cells  are  not  so  exceedingly  profuse.  l    fiy\_£ 

The  parietal-cells  can  be  recognized  with  the  low  power  ^'-^'Y 

as  isolated  red  spots  on  a  rosy-red  ground.      With  the  r" ' 

high  power  the    pale   blue    smaller  chief-cells  can  be  '' 

seen.  The  very  narrow  lumen  of  the  fundus  glands  may 
be  best  seen  in  cross-sections  of  the  follicle  (sections 
parallel  to  the  surface  of  the  mucosa).  The  lateral 
twigs  of  the  chief  lumen  can  only  be  perceived  in 
very  favorable  sections  (Fig.  134).  Fig.  133  is  a  com- 
bination of  several  thin  longitudinal  sections. 

b.  For  pylonis  glands,  stain  vertical  and  horizontal 
sections  of  the  mucosa  with  Bohmer's  hematoxylin  and 
mount  in  damar.     The  lumen  of  the  pyloric  glands  is 

wider  (Fig.  136).  ^t^ 

No.  103. —  Brunner  s  Glands. — Cut  out  the 
stomach  and  duodenum  of  a  cat  about  i  hour  after 
death.  Open  both  along  their  length,  remove  the  con- 
tents by  swaying  them  gently  to  and  fro  in  salt  solution 

(p.  19),  and  place  the  pyloric  end  of  the  stomach  and  the  upper  half  of  the 
duodenum,  that  is,  in  all  a  piece  5  to  6  cm.  long,  for  6  hours  in  100  c.c. 
3  per  cent,  nitric  acid.  Further  treatment  like  No.  99.  Cut  longitudinal 
sections,  which  pass  simultaneously  through  the  pylorus  and  duodenum.  Stain 
with  Bohmer's  hematox\lin.  Mount  in  glycerine  or  in  damar  (Fig.  136).  If 
the  tissue  be  placed  in  the  acid  immediately  after  death  the  smooth  muscle  of 
the  intestine  contracts  so  that  a  rigid  curving  of  the  intestinal  wall  takes 
place. 

No.  104. — Epilhclium  and  Villi  of  the  Small  Intestine. — From  the  small 
intestine  of  a  rabbit  just  killed,  cut  a  jiiece  i  cm.  long,  open  it  along  its  length 
and  remove  the  contents  by  carefully  pouring  over  it  i/^  per  cent,  salt  solution. 
Then  grasp  the  piece  at  the  left  edge  with  the  forceps,  with  fine  scissors  cut  off 
a  small  strip,  and  spread  it  out  in  a  drop  of  salt  solution  on  a  slide  on  a  black 
background.  With  the  unaided  eye  one  can  see  the  villi  projecting  froni  the 
edge  of  the  preparation.  Examine  the  preparation  without  a  cover-f;lass, 
with  the  low  power.     The  villi  will  be  seen  partly  extended,  partly  contracted  ; 


Fic. 

265.- 

-LOWBR 

Half 

OP 

AN 
clii 

Iso 

!"  B 

ef-ccll 

OF      Ra) 

Haricl:.: 

hUNUUS- 

BBir.       X 
l-ccll;   M, 

304  HISTOLOGY. 

the  latter  condition  may  be  recognized  by  transverse  folds  running  across  the 
villi  (Fig.  266).  Details  cannot  be  detected.  Apply  a  cover-glass;  the 
villi  thus  become  flattened  and  appear  clearer;  the  cylindrical  epithelium,  and 
close  beneath  this  the  loops  of  the  capillary  blood-vessels,  can  be  distinctly  seen. 
If  the  epithelium  contains  goblet-cells,  these  appear  as  bright  shining  rounded 
spots.      For  the  investigation  of  the  epithelium,  proceed  as  follows  :  — 

a.  Tease  the  piece  a  little  ;  in  this  way  columnar  cells,  singly  and  in 
groups,  may  be  isolated,  which  are  to  be  examined  with  the  high  power.  Not 
infrequently  a  few  columnar  cells  are  found  inflated  and  of  a  spherical  form.  The 
basal  border  sometimes  shows  very  distinct  rods.  Goblet-cells,  when  present, 
may  be  recognized  by  their  homogeneous  appearance,  and  if  carefully  focused 
the  sharply-outlined  orifice  may  be  perceived.  Occasionally  the  epithelial  cells 
are  difficult  to  loosen  from  the  basement-membrane  ;  in  such  cases  make  a  sec- 
ond investigation  an  hour  later,  when  the  epithelium  will  be  suificiently  macer- 
ated to  be  brushed  off. 

/'.  F"or  permanent  preparations  place  pieces  (  i  cm.  square)  of  the  intes- 
tine in  30  c.c.  of  Miiller's  fluid.  In  3  to  5  days  take  the  tissue  out,  scrape  it 
with  the  tip  of  a  scalpel,  and  distribute  a  little  of  the  scraping  in  a  drop  of 
diluted  glycerine  ;  cover-glass;  high  power  (Fig.  139,  K). 

No.  lot;. — Secfioiis  of  the  Small  Intestine. — Place  pieces  2  to  4  cm.  long 
of  the  intestine  of  a  rabbit,  better,  of  a  puppy  or  a  kitten,  in  100  to  200  c.c. 
of  3  per  cent,  nitric  acid.     After  6  hours  the  pieces  are 
to  be  hardened  in   100  c.c.  of  gradually  strengthened 
alcohol.     Sections  can  be  made  through  the  entire  in- 
testinal tube  ;   in  most  cases,  only  fragments  of  the  villi 
are  thus  obtained  ;  to  obtain  entire  villi  cut  ojien  the 
hardened  intestine  along  its  length  with  a  razor,  pin  it 
with  needles  on  a  cork-plate,  with  the  mucosa  upper- 
most.    The  villi  can  then   be  seen   with   the  unaided 
eye.       Cut    thick    cross-sections,    stain    them    for   one. 
minute    with    Bohmer's   hemato.xylin,    and    mount   in 
daraar.      Goblet-cells  are  very  frequently  found  in  the 
epithelium    (Fig.    139,    B).       Staining    in    bulk    with 
borax-carmine  is  to  be  strongly  recommended. 
The  human  intestine,  before  being  placed  in  the  nitric  acid,  must  be  cut 
open  and  washed  in  the  same  fluid.      It  is  advisable  to  pin  pieces  about  5  cm. 
square  to  a  cork-plate  and  thus  to  place  them  in  the  fixing  and  hardening  fluids. 
If  the  intestine  is  not  absolutely  fresh,  the  entire  superficial  epithelium  loosens 
so  that  the  naked  connective-tissue  villi  lie  exposed. 

Horizontal  sections  of  the  intestine  furnish  very  beautiful  pictures.  Not 
infrequently  the  cross-sections  of  the  glands  drop  out  and  then  only  the  con- 
nective-tissue tunica  propria  remains.  In  these  preparations  the  goblet-cells  all 
appear  as  clear  bodies  of  equal  size,  and  therefore  afford  no  clue  in  regard  to 
the  functional  condition  of  the  cell. 

For  the  latter  purpose  the  following  is  to  be  recommended  :— 

No.  106. — -Triple  Staining  of  the  Intestine. — Small  pieces  of  tissue  are  to 
be  fixed  in  Flemming's  mixture  (p.  21),  hardened  in  gradually  strengthened 
alcohol,  and  subsequently  treated  according  to  the  method  given  on  p.  34,  10. 

No.  107. — The  Patches  of  Fever. — These  can  be  seen  shimmering 
through  the  uninjured  fresh  intestinal  wall  of  the  rabbit,  but  in  the  dog  and 
in  the  cat  they  are  often  (on  account  of  the  thickness  of  the  muscular  coat) 
not  at  all  perceptible.      In  the  latter  animals  patches  are  constant  at  the  point 


SPECIAL    lECHNIuLE.  305 

where  the  small  intestine  opens  into  the  large.  Cut  out  the  portion  of  the 
intestine  of  a  rabbit  containing  the  Peyer's  patches  and  proceed  according  to 
the  method  given  in  No.  105.  In  the  cat  take  the  lowermost  portion  of  the 
ileum  (about  2  cm.  long)  with  a  piece  of  the  cecum  of  the  same  length  ;  open 
both  along  their  length  and  span  them  out  on  a  cork-plate,  with  the  muco.sa 
uppermost.  Usually  the  mucosa  is  covered  with  a  tenaceous  excrement,  dif- 
ficult to  remove  by  washing,  and  which  glues  the  villi  together,  so  that  only 
oblique  sections  of  the  villi  can  be  obtained.      Further  treatment  like  No.  105. 

Closely-placed  nodules  are  found  in  the  blind  half  of  the  vermiform  pro- 
cess of  the  rabbit,  which  encroach  upon  the  muco.sa  and  compress  it  to  such 
narrow  areas  that  cross-sections  exhibit  very  complicated  pictures,  scarcely  in- 
telligible to  the  beginner. 

Fi.xation  in  o.i  per  cent,  chromic  acid  and  hardening  in  gradually 
strengthening  alcohols  renders  the  germinal  centers  very  distinct,  but  is  not 
so  good  for  the  remaining  elements  as  the  nitric  acid. 

No.  108. —  The  Large  Intestine. — Treat  empty  pieces  like  No.  105  or 
106  (compare  with  Fig.  13,  p.  59).  Pieces  filled  with  feces  must  be  cut  open, 
washed,  and  spanned  on  cork. 

No.  109. — Fresh  Crypts  of  the  Large  Intestine  (yf  the  Rahhit. — Cut  a  piece 
I  cm.  long  from  the  lowermost  portion  of  the  large 
intestine  (between  two  s])herical  masses  of  feces )  place 
it  on  a  dry  slide,  open  it  with  the  scissors,  and  spread 
it  out  with  the  mucous  surface  uppermost  ;  add  a  drop 
of  J4^  per  cent,  salt  solution,  grasp  the  piece  with  for- 
ceps at  the  left  edge,  and  with  fine  scissors  cut  off  an 
extremely  thin  strip.  Transfer  this  with  a  drop  of  the 
salt  solution  to  another  slide  ;  with  needles  se])arate  the 
muscularis  from  the  mucosa  and  tease  the  latter  a  very 
little;  apply  a  cover-glass  with  slight  pressure.  \\'ith 
a  low  power  the  follicles  of  the  crypts  can  be  readily 
seen,  but  it  is  difficult  to  detect  their  orifices  ( F"ig. 
267).  The  epithelial  cells  are  often  granular  in  the  '"ryptJ of''Lieberkah " '  x 
portion  bordering  the  lumen.  With  the  high  power  the  ^°- 
superficial   eiiithelium   can   be  very  well  seen  from  the 

side  and  from  the  surface.  The  contents  of  the  goblet-cells  are  often  not 
clear,  as  in  sections,  but  dark  and  granular. 

No.  no. — Bloihi-vessels  of  the  Stomaeh  anJ  the  Intestines. — A  stomach  and 
intestine  injected  from  the  descending  aorta,  are  to  be  fi.xed  in  50  to  200  c.c.  of 
Miiller's  fluid  and  hardened  in  gradually  strengthened  alcohols.  One  portion 
should  be  cut  into  thick  (up  to  i  mm.)  sections,  stained,  and  mounted  in 
daniar  (Fig.  144),  and  another  part  used  for  horizontal  preparations,  which  with 
the  low  power  and  change  of  focus  are  very  instructive.  For  this  purpose  pieces 
of  the  large  intestine,  i  cm.  square,  may  be  transferred  from  absolute  alcohol  to 
5  c.c.  of  turpentine  for  clearing,  and  mounted  in  damar.  It  is  easy  to  strip 
the  muscularis  from  the  mucosa  and  to  mount  the  separate  coats  in  damar. 

No.  III. — Aiierbach'  s  and  Meissnei'  s  Ple.xtis. — For  this  purpose  the  intes- 
tine of  the  rabbit  and  guinea-pig  (not  of  the  cat)  are  especially  suitable.  It  is 
not  necessary  that  the  object  be  absolutely  fresh  ;  the  small  intestines  of  chil- 
dren several  days  after  death  can  still  be  used.  Prepare  200  c.c.  of  a  dilute 
solution  of  acetic  acid  (10  drops  of  glacial  acetic  acid  to  200  c.c.  of  distilled 
water).  Then  separate  a  piece  (10  to  30  cm.  long)  of  the  small  intestine  from 
the  mesentery.     Cut  it  open  and  brush  out  the  contents  lightly  with  the  finger ; 


3o6  HISTOLOGY. 

tie  the  lower  end  of  the  intestine  and  fill  it  from  the  upper  end  with  the 
diluted  acetic  acid  ;  tie  it  above  and  place  the  whole  piece  in  the  remainder  of 
the  acetic  acid.  In  i  hour  change  the  fluid.  In  24  hours  transfer  the  intes- 
tine to  distilled  water,  with  scissors  open  it  along  one  side  of  the  line  of  attach- 
ment of  the  mesentery,  and  cut  off  a  piece  1  cm.  long.  The  muscularis  can 
be  readily  separated  from  the  mucosa  with  the  aid  of  forceps ;  they  are  only 
firmly  united  at  the  line  of  attachment  of  the  mesentery. 

a.  AuerbacJi  s  Plexus. — If  a  piece  of  black  paper  be  placed  under  the  glass 
dish  containing  the  tissue,  the  white  nodal  points  of  Auerbach's  plexus  can  be 
seen  by  the  unaided  eye.  Transfer  a  piece  of  the  muscularis,  about  i  cm.  square, 
in  a  drop  of  the  diluted  acetic  acid  to  a  slide  ;  examined  with  the  low  power  it 
furnishes  a  very  pretty  picture  (Fig.  145,  A).  If  it  is  desired  to  preserve  the 
preparation,  place  the  tissue  for  i  hour  in  30  c.c.  of  distilled  water,  which  must 
be  changed  several  times,  and  then  for  from  8  to  16  hours  in  5  to  10  c.c.  of  a  i 
per  cent,  osmic  acid  solution,  in  /he  dark  ;  wash  the  piece  quickly  in  distilled 
water  and  mount  in  diluted  glycerine.  The  osmium  preparations  are  not  as 
beautiful  as  the  fresh  ones  in  the  acetic  acid.  In  the  guinea-pig  both  strata  of 
the  muscularis  can  be  readily  separated  (if  the  intestine  is  absolutely  fresh  on 
being  filled  with  the  dilute  acid)  :  the  plexus  remains  attached  to  one  stratum. 
Pieces  of  this  should  be  placed  for  i  hour  in  distilled  water,  then  treated  with  gold 
chloride  (p.  37),  and  mounted  in  damar.  The  gold-chloride  treatment  is  less 
adapted  to  human  intestines,  since  both  the  muscular  layers  are  likewise  stained 
red  and  partially  conceal  the  plexus.  The  firm  union  of  the  muscular  strata  in 
the  human  organ  may  be  due  to  the  age  of  the  object. 

b.  Afeissner's  Plexus. — With  a  scalpel  scrape  the  epithelium  from  the 
isolated  mucosa  ;  place  a  piece  about  i  cm.  square  on  a  slide  ;  apply  a  cover- 
glass,  press  upon  it  slightly,  and  examine  with  the  low  power  (Fig.  145,  B). 
To  preserve  the  preparation,  proceed  as  in  No.  in,  a;  but  it  is  advisable  to 
span  the  pieces  on  cork  and  before  transferring  them  from  the  absolute  alcohol 
to  the  bergamot  oil,  to  press  them  somewhat,  in  order  that  the  alcohol  may  be 
completely  removed  from  the  spongy  mucosa. 

In  addition  to  nerves,  many  blood-vessels  are  present,  which  may  be  easily 
recognized  by  the  structure  of  their  walls,  in  part  by  the  transversely-placed 
nuclei  of  the  muscle-fibers. 

No.  112. —  The  Parotid,  Siil/maxillary,  and  Sublingual  Glands. — From 
human  glands  (still  useful  in  winter  after  3  or  4  days)  cut  a  number  of  pieces 
0.5  to  I  cm.  square,  and  place  them  in  30  c.c.  of  absolute  alcohol,  which  should 
be  changed  in  5  to  20  hours.  In  3  days  the  tissues  are  ready  to  be  sectioned, 
and  can  be  used  at  once  or  later.  Stain  i  piece  in  bulk  in  borax-carmine. 
Embed  another  in  liver  and  cut  the  thinnest  possible  sections  ;  small  fragments 
about  2  mm.  long  can  be  used  ;  stain  them  in  Bohmer's  hematoxylin,  2  to  3 
minutes ;  the  transfer  of  the  sections  to  the  staining  solution  must  be  done 
slowly,  or  the  most  delicate  sections  will  be  destroyed  ;  then  stain  with  eosin 
(p.  32),  and  mount  in  damar.  (Very  thin  sections  should  be  examined  in 
water  after  the  staining  in  hematoxylin  is  completed,  since  the  cell  boundaries 
are  then  very  much  more  distinct.)  If  the  staining  is  successful,  the  salivary 
tubules  and  the  crescents  are  red.  In  the  sublingual  gland  and  in  the  mucous 
cells  of  the  submaxillary  the  membrana  propria  also  stains  red  ;  it  must  not  be 
confused  with  the  sections  of  the  crescents,  which  latter  are  granular,  while  the 
membrana  propria  has  a  homogeneous  appearance.  The  mucous  cells  in  the 
borax -carmine  preparations  are  clear  throughout.  In  the  sections  stained  with 
hematoxylin  they  are  sometimes  clear,  sometimes  a  pale  blue  of  different 
shades  (Fig.  146)  ;  the  portion  which  stains  is  a  reticulum  which  occurs  in 


SPECIAL    TECHNKJfE.  307 

certain  functional  stages  of  each  mucous  cell.  The  very  short  intercalated 
pieces  of  the  submaxillary  gland  are  difficult  to  find  ;  on  the  other  hand,  they 
may  be  easily  seen  in  the  parotid  (also  in  that  of  the  rabbit).  Of  the  end- 
pieces  only  certain  portions,  those  which  have  been  accurately  halved  and  the 
lumen  of  which  is  visible,  are  suitable  for  study.  The  numerous  oblique  and 
tangential  sections  are  often  very  difficult  to  understand  (Fig.  146,  4,  5,  6,  7). 

No.  113. — The  Pancreas. — The  human  pancreas  as  a  rule  cannot  be  used. 
The  treatment  is  the  same  as  for  the  parotid  gland,  Xo.  112.  The  character- 
istic granular  zone  of  the  gland-cells,  bordering  the  lumen,  is  not  to  be  seen 
by  this  method  (Fig.  149.  B).  Tease  a  i)inhead-sized  piece  of  the  fresh  pan- 
creas of  a  cat  in  a  drop  of  Y^  per  cent,  salt  .solution.  With  the  low  power  the 
acini  appear  spotted  ;  this  is  due  to  the  partly  clear  and  partly  granular  divi- 
sions of  the  cell.     With  high  magnification  the  tissue  appears  like  Fig.  149,  A. 

No.  114. — Liver  Cells. — Make  an  incision  in  a  fresh  liver  and  with  the 
blade  of  the  scalpel  obliquely  placed  scrape  the  cut  surface.  The  brown  liver- 
tissue  attached  to  the  blade  is  to  be  transferred  to  a  slide  and  a  drop  of  salt 
solution  added.  Apply  a  cover-glass.  Examine  first  with  the  low  power 
then  with  the  high  (Fig.  153,  A).  The  jireparation  contains,  in  addition  to 
the  liver-cells,  numerous  colored  and  colorless  blood -corpuscles. 

Xo.  115. — Hepatic  Lobules. — Place  small  pieces  (about  2  cm.  cubes)  of 
a  l)ig's  liver  in  30  to  50  c.c.  of  absolute  alcohol.  The  majority  of  the  lobules 
are  hexagonal  ;  they  can  be  seen  on  the  surface  of  the  liver  by  the  unaided  eye, 
and  after  a  moment  become  distinctly  visible  on  the  cut  surface.  The  section 
of  the  central  vein  also  becomes  visible.  In  about  3  days  sections  can  be 
made  ;  stain  them  with  Bohmer's  hematoxylin.  The  division  into  lobules  can 
be  well  seen  with  the  low  |)ower,  but  the  hepatic  cells  as  well  as  the  bile-ducts 
are  less  satisfactory  for  study.      Better  for  this  purpose  is  the  following. 

No.  116. — Human  Liver. — Place  pieces  about  2  cm.  square,  as  fresh  as 
possible,  for  4  weeks  in  200  c.c.  of  Miiller's  fluid  for  fixation  and  then 
in  100  c.c.  of  gradually  strengthened  alcohols  for  hardening.  Examine 
unstained  sections  (parallel  and  also  vertical  to  the  surface)  and  stain  others 
with  Bohmer's  hematoxylin  and  also  with  eosin  ;  mount  in  damar.  The  de- 
marcation of  the  lobules  is  not  distinct,  because  of  the  slight  development  of 
the  interlobular  connective  tissue.  The  division  into  lobules  may  be  more 
readily  perceived  on  macroscopic  inspection,  than  on  investigation  with  the 
microscope.  For  orientation  the  beginner  should  recall  that  isolated  sections  of 
blood-vessels  always  represent  intralobular  veins  ;  while  numbers  of  sections 
together  rejiresent  branches  of  the  ])ortal  vein,  of  the  he|)atic  artery,  and  of 
the  bile-duct.  Exact  transverse  sections  of  central  veins  may  also  be  recog- 
nized by  the  cords  of  hepatic  cells  radiating  from  them  (Fig.  154).  For  the 
study  of  the  structure  of  the  gall-bladder  as  well  as  of  the  larger  bile-ducts, 
only  absolutely  fresh  livers  can  be  used,  since  the  alkaline  bile  permeates  the 
walls  of  the  gall-bladder  soon  after  death,  stains  the  tissue  yellow,  and  renders 
it  unfit  for  microscopic  investigation. 

Xo.  117. — To  demonstrate  iht:  capillaries  astd  X\\t  intralobular  connective 
tissue,  which  in  ordinary  preparations  are  scarcely  visible,  shake  a  number  of 
thin  double-stained  sections  of  human  liver  (Xo.  116)  for  from  2  to  3  minutes 
in  a  test-tube  half  filled  with  distilled  water.  The  liver-cells  in  part  fall  out: 
the  edges  of  the  preparation  are  then  to  be  examined  in  a  drop  of  water  (Fig. 
163).  This  preparation  can  be  mounted  in  damar,  but  the  more  delicate  con- 
nective-tissue fibers  disappear  therein. 


3o8  HISTOLOGY. 

No.  1 18. — Blood-  Vessels  of  the  Liver. 

a.  Chloroform  a  rabbit  and  quickly  place  a  2  cm.  cube  of  the  liver  (with- 
out allowing  much  blood  to  flow  from  it)  in  50  c.c.  of  absolute  alcohol.  In  2 
days  the  natural  injection  can  be  seen  on  the  surface ;  it  is  indicated  by  brown 
spots  within  the  centers  of  the  lobules.  Cut  thick  sections  parallel  to  the  sur- 
face, and  mount  them  unstained  in  damar.  Examine  with  a  low  power. 
Very  frequently  only  the  superficial  strata  of  the  liver  contain  filled  blood- 
vessels. 

/'.  Of  all  injections  that  of  the  liver  is  most  easily  accomplished.  Inject 
Berlin  blue  (p.  37),  either  through  the  [lortal  vein  or  the  inferior  vena  cava; 
in  the  latter  case  it  is  advisable  to  make  an  incision  above  the  diaphragm,  to 
allow  the  heart  to  rest  upon  it,  and  to  insert  the  canula  through  the  right  auri- 
cle into  the  inferior  cava.  The  injected  liver  is  to  be  placed  in  toto  in  about 
500  c.c.  of  Miiller's  fluid  ;  after  6  days  pieces  about  2  cm.  square  of  the  por- 
tions best  injected  are  to  be  cut  out,  placed  again  for  2  to  3  weeks  in  about  150 
c.c.  of  Miiller's  fluid,  and  finally  hardened  in  100  c.c.  of  gradually  strengthened 
alcohols.  Cut  thick  sections  and  mount  them  unstained  in  damar  (Fig.  157, 
158,  159)- 

No.  119 — Exhibition  of  Glaiui  Lumina  hv  Golgi's  '^ Black  Reaction.''' — 
Place  small  pieces  of  stomach,  of  salivary  glands,  and  of  liver  for  3  days  in  the 
osmio-bichromate  mixture  (in  winter,  in  the  warm  chamber,  p.  36),  and  for  the 
same  length  of  time  in  the  silver  solution.  For  further  treatment  see  p.  35. 
Very  often  the  staining  does  not  succeed  until  after  the  procedure  has  been 
reiieated  once  or  twice.  After-staining  (p.  37)  is  to  be  advised.  In  the  liver  the 
"lattice-fibers"  stain  occasionally. 

No.  1 20.  —  The  Endothelium  of  the  Peritoneum. — Proceed  as  in  No.  35,  but 
instead  of  taking  the  mesentery,  which  also  yields  instructive  pictures,  use  the 
greater  omentum.  The  pieces  may  be  stained  in  Bohmer's  hematoxylin  and 
mounted  in  damar  (Fig.  167). 

No.  121.  —  The  Connective-tissue  Reticulum. — This  may  be  obtained  by 
spreading  out  a  fragment  of  a  fresh  human  omentum  in  a  few  drops  of  picro- 
carmine.     Mount  in  diluted  glycerine  (not  acidulated). 


XIII.  THE  RESPIRATORY  ORGANS. 

No.  122. — The  Larynx,  the  Bronchi,  and  the  Thyroid  Gland. — Of  animals, 
the  cat  is  especially  suitable.  Expose  the  bronchi  above  the  manubrium, 
cut  them  and  the  esophagus  through  transversely  and  dissect  both  loose 
upwards  (see  No.  97).  The  tongue  maybe  removed  with  these  parts.  The 
thyroid  gland  should  be  allowed  to  remain  attached  to  the  larynx.  The  whole 
is  to  be  placed  for  from  2  to  6  weeks  in  200  to  400  c.c.  of  Miiller's  fluid,  then 
washed  for  i  hour  in  running  water  and  hardened  in  200  c.c.  of  gradually 
strengthened  alcohol.  In  about  8  days  cut  sections,  transverse  and  longitu- 
dinal, through  the  vocal  cords  and  portions  of  the  trachea  ;  stain  them  for  5 
minutes  in  Bohmer's  hematoxylin,  and  mount  in  damar.  Especially  instructive 
are  sections  taken  transversely  through  the  vocal  cords,  in  which  the  mucous 
membrane,  glands,  muscles,  blood-vessels,  nerves,  and  cartilage  furnish  material 
for  the  most  varied  study. 

No.  133.  —  The  Bronchi. — From  an  animal  just  killed  (rabbit)  remove  the 
lungs,  fix  them  in  Miiller's  fluid  and  harden  them  in  gradually  strengthened 
alcohol,  like   No.   122.     In  8  davs  cut  out  of  the  lung    i   cm.  cubes,  which 


SPECIAL    TECHNIQUE.  309 

contain  a  portion  of  a  longitudinally-disposed  bronchus.  With  the  scissors 
remove  the  greater  part  of  the  attached  lung  tissue  ;  embed  the  bronchus  in 
liver,  and  make  thin  transverse  sections,  which  may  be  stained  in  Bohmer's 
hematoxylin  and  mounted  in  daniar  (Fig.  i68).  The  lungs  of  cat.s  are  less 
suitable  than  those  of  the  rabbit,  owing  to  the  often  considerable  masses  of  fat 
surrounding  the  bronchi.  This  method  is  also  applicable  for  the  exhibition  of 
the  alveoli  and  the  alveolar  pa.ssages. 

Xo.  124. — The  Respiratory  Epithelium. — For  the  demonstration  of  this  tis- 
sue only  animals  just  killed  can  be  used.  Young  kittens  (not  newborn)  are 
suitable  ;  they  should  be  killed  by  decajiitation.  The  trachea  and  lungsshould 
then  be  carefully  taken  out  and  filled  by  means  of  a  glass  pipet  with  a  previously- 
prepared  solution  of  silver  nitrate  (  50  c.c.  of  a  i  per  cent,  solution  to  200  c.c. 
of  distilled  water).  The  trachea  should  then  be  tied  fast  and  the  whole  placed 
(  I  to  12  hours)  in  the  remainder  of  the  silver  solution  and  stood  in  the  dark. 
On  removing  them  from  the  silver  solution,  the  lungs  should  be  quickly 
washed  with  distilled  water  and  transferred  to  150  c.c.  of  gradually 
strengthened  alcohol,  in  which  they  may  remain  (in  the  dark)  for  an  indefinite 
length  of  time.  The  reduction  can  be  undertaken  in  an  hour  after  the  silver 
injection,  or  later.  For  this  purpose  the  lungs  in  the  alcohol  should  be  exposed 
to  sunlight,  in  which  they  become  a  deep  brown  in  a  few  minutes.  With  a  zvvt 
sharp  razor  cut  thin  sections,  taking  care  not  to  compress  the  tissue.  Despite  the 
hardening  in  alcohol  the  lung  tissue  is  still  soft  and  allows  only  thick  sections 
to  be  cut.  Sections  may  be  most  easily  cut  in  a  direction  parallel  to  the  surface. 
Place  the  sections  for  from  10  to  60  minutes  in  5  to  10  c.c.  of  distilled  water 
to  which  a  crystal  of  common  salt  about  the  size  of  a  lentil  has  been  added, 
and  then  mount  them  unstained  indamar.  It  is  not  advisable  to  employ  nuclear 
staining,  since  not  only  the  nuclei  of  the  epithelial  cells,  but  also  those  of  the 
cai)illaries  and  other  tissues  are  colored,  and  consequently  the  picture  becomes 
very  complicated.  Orientation  in  such  .sections  is  not  altogether  easy.  The 
investigation  should  be  begun  with  the  low  power.  The  small  alveoli  are  easily 
recognized  ;  the  somewhat  larger  spaces  correspond  to  alveolar  ducts.  The 
demarcation  of  the  epithelium  is  on  the  whole  finer  with  medium  magnification 
(So  diameters ),  and  by  no  means  eciually  good  in  all  places.  The  cubical 
epithelial  cells  are  usually  colored  a  somewhat  deeper  brown.  Find  a  good 
place,  study  it  with  the  high  power  (240  diameters),  and  by  changing  the  focus 
(elevating  and  depressing  the  tube)  note  the  relief  of  the  preparation  ;  with 
high  magnification,  either  only  the  ba.se  or  the  edge  of  an  alveolus  can  be  dis- 
tinctly seen.      Fig.  170  was  drawn  with  change  of  focus. 

Xi).  125. — Elastic  Fibers  of  the  Lungs. — With  the  scissors  placed  flatwise 
on  the  lung  (the  lung  need  not  be  fresh  ),  cut  a  flat  piece  i  cm.  square,  spread 
it  out  with  needles  on  a  dry  slide,  apply  a  cover-glass  and  treat  with  2  drops 
of  potash  lye  diluted  'j  with  water  ;  the  diluted  lye  destroys  all  parts  except- 
ing only  the  elastic  fibers,  who.se  thickness  and  arrangement  may  l)e  easily  in- 
vestigated with  the  high  i)ower  (240  diameters).  * 

Xo.  126. — Blood-vessels  of  the  Lungs. — Inject  the  lung  from  the  pulmo- 
nary artery  with  Herlin  blue  ;  fix  it  in  Miiller's  fluid,  and  harden  it  in  alcohol. 
Cut  thick  sections,  principally  parallel  to  the  surface  of  the  lung  (Fig.  171). 

Xo.  127. —  The  Thyroiii  Gland. — Thin  sections  of  the  gland,  hardened  in 
toto  (see  No.  122  ),  are  to  be  stained  with  picrocarmine  and  mounted  in  damar 
(Fig.  172).  The  retracted  colloid  ma.sses  stain  an  intense  yellow.  Examine 
thick  sections  in  glycerine,  in  which  the  lyniiih-vessels  filled  with  colloid  sub- 
stance are  often  distinctly  visible. 


3IO  HISTOLOGY. 

No.  128.  —  The  Thymus  Body. — Place  the  thymus  body  of  a  young  animal, 
for  from  2  to  5  weeks,  in  Miiller's  fluid  and  harden  it  in  gradually  strengthened 
alcohol.  Stain  sections  with  Bohmer's  hematoxylin  ;  mount  them  in  damar 
(Fig.  173).  Care  should  be  taken  not  to  confuse  the  cross-sections  of  the 
blood-vessels,  the  lumina  of  which  change  in  elevating  and  depressing  the  tube 
(when  they  are  not  true  cross-sections),  with  the  concentrically-striated  cor- 
puscles of  Hassall.  The  preparation  represented  in  Fig.  174  is  from  a  thymus 
bodv  fixed  in  Flemming's  mixture  and  stained  with  safl'ranin. 

XIV.  THE  URINARY  ORGANS. 

No.  129. — Isolated  Urinifemis  Tubules. — The  most  suitable  for  this  pur- 
pose are  the  kidneys  of  young  animals,  for  example  newborn  kittens.  Divide 
the  kidney  in  halves  ;  place  one  half  (<?)  aside  for  investigation  fresh  ;  cut  the 
other  half  (^F)  into  pieces  including  the  cortex  and  medulla,  and  place  them  in 
30  c.c.  of  pure  hydrochloric  acid. 

a.  Tease  a  pea-sized  piece  in  a  drop  of  0.75  per  cent,  salt  solution.  The 
red  glomeruli,  the  convoluted  and  straight  uriniferous  tubules,  can  be  seen 
with  the  low  power.  The  convoluted  tubules  are  dark  and  granular,  the 
other  divisions  clear.  With  high  magnification,  the  nuclei  of  the  clear  por- 
tion of  the  uriniferous  tubules  can  be  distinctly  seen  ;  the  cell  boundaries  may 
best  be  seen  in  the  collecting  tubules.  In  the  convoluted  tubules  only  the  fine 
striation  of  the  bases  of  the  gland-cells  can  be  seen  ;  cell  boundaries  and  nuclei 
are  not  visible. 

b.  In  about  2  hours  the  red  pieces  of  kidney  tissue  should  be  transferred  to 
a  capsule  containing  50  c.c.  of  distilled  water,  in  which  they  rapidly  turn  a  dirty 
gray  and  acquire  smeary  surfaces.  The  water  is  to  be  changed.  After  a 
few  moments  small  pieces  can  be  detached  with  needles  and  readily  separated 
into  tubules,  in  a  little  water  on  a  slide.  If  it  is  desired  to  obtain  entire 
uriniferous  tubules,  transfer  pieces  of  kidney  2  cm.  square  to  a  watch-glass  in 
which  has  been  placed  a  cover-glass  and  enough  distilled  water  to  cover  the 
surface  of  the  latter.  The  tubules  should  now  be  isolated  with  needles.  If  the 
isolation  is  successful — this  may  be  ascertained  by  examination  with  low  power 
— -carefully  absorb  with  filter-paper  the  water  from  the  watch-glass  and  then 
from  the  cover-glass,  take  out  the  latter,  cleanse  its  free  surface,  and  place  it 
with  the  attached  tubules  gently  on  a  slide  on  which  a  drop  of  dilute  glycerine 
has  been  previously  placed.  The  preparation  may  be  subsequently  stained 
under  the  cover-glass  with  picrocarmine  (Fig.  176). 

No.  130.  —  The  Cortex  and  MeduUa. — For  sections  the  kitten's  other 
kidney  or  other  pieces  of  kidney  tissue  2  to  3  cm.  square  are  to  be  fixed  in  200 
to  300  c.c.  of  Miiller's  fluid,  and  in  4  weeks  hardened  in  100  c.c.  of  gradually 
strengthened  alcohol.  Fixation  in  absolute  alcohol  (like  No.  132)  is  still 
better.  Thick  transverse  and  longitudinal  sections  through  the  cortex  and 
similar  ones  through  the  medulla  are  to  be  examined  unstained  in  dilute  gly- 
cerine, with  a  low  power.  Thin  transverse  sections  through  the  apex  of  the 
papilla;,  through  the  base  of  the  papillae  for  the  excretory  duct  (Fig.  181),  and 
through  the  cortex  are  to  be  stained  with  Bohmer's  hematoxylin  and  mounted 
in  damar.  Endeavor  to  cut  sections  through  the  cortex  and  the  medulla, 
showing  the  boundary  between  the  two ;  examine  them  unstained  in  glycerine, 
with  the  low  power.  Frequently  the  blood-vessels  are  still  filled  with  blood- 
corpuscles  and  may  be  traced  for  long  distances. 

No.  131. — Medullary  rays  and  Henle^ s  loops  are  especially  fine  in  stained 
vertical  sections  of  the  kidneys  of  young  animals  treated  like  No.  130. 


SPECIAL   TECHNlgUE.  3II 

No.  132. — For  the  study  of  Unt  glomeruli  and  Bowman' s  capsule,  also  the 
connection  of  the  latter  with  the  uriniferous  tubule,  the  kidney  of  the  mouse 
is  most  suitable.  Fi.\  and  harden  the  divided  kidney  in  15  c.c.  'of  absolute 
alcohol,  which  should  be  changed  in  an  hour-  After  3  days  (or  later)  cut  thin 
sections  of  the  cortex,  stain  2  to  3  minutes  in  Bohmer's  hematoxylin,  and  mount 
in  dauiar  (Fig.  179).  The  invaginated  jjortion  of  the  capsule,  on  account  of 
the  similarly-stained  nuclei  of  the  blood-vessel  walls,  cannot  be  distinguished. 
The  appearance  of  the  cells  in  the  varying  phases  of  .secretion  can  only  be  in- 
vestigated in  the  absolutely  fresh  object  fixed  in  Flemming's  mixture  (p.  21), 
and  cut  in  very  thin  sections. 

No.  133. — The  Blood-vessels  of  the  Kidney. — .\n  isolated  kidney  may  be 
injected  (p.  37)  and  fixed  in  300  c.c.  of  Miiller's  fluid  for  4  weeks  and  then 
hardened  in  150  c.c.  of  gradually  strengthened  alcohol.  The  venae  stellata; 
can  be  investigated  macroscopically.  Unstained  thick  longitudinal  and  trans- 
verse sections  should  be  studied  with  the  low  power  (Fig.  182 ). 

No.  134. — Nerves  of  the  Kidney. — Treat  small  pieces  according  to  the 
method  given  on  p.  35  ;  they  should  remain  3  to  6  days  in  the  osmio-bichro- 
mate  mixture. 

No.  135. — The  Pelvis  of  the  Kidney  and  Ureters. — Of  the  former  pieces 
I  cm.  square,  of  the  latter  i  to  2  cm.  long  should  be  fixed  in  Miiller's  fluid, 
and  in  14  days  hardened  in  100  c.c.  of  gradually  strengthened  alcohol.  Stain 
sections  with  Bohmer's  hematoxylin  and  mount  in  damar. 

No.  136.— Treat  the  j9/<f<Mv- like  No.  135. 

No.  137. — Epithelial  Cells  of  the  Pelvis  of  the  Kidney,  the  Ureter,  and 
the  Bladder. — Place  pieces  of  these  parts,  i  cm.  square  (cut  open  the  ureter), 
in  30  c.c.  of  Ranvier's  alcohol.  Isolate  and  stain  with  picrocarmine.  Mount 
in  diluted  acidulated  glycerine. 

No.  138.  —  The  Female  Urethra. — Cut  out  a  piece  of  the  female  urethra 
about  2  cm.  long,  together  with  the  attached  anterior  vaginal  wall  ;  place  it  in 
100  to  200  c.c.  of  Miiller's  fluid  for  fixation,  and  in  2  to  3  weeks  harden  it  in 
gradually  strengthened  alcohol  (]).  29).  Stain  cross-sections  in  Bohmer's 
hematoxylin  (p.  31  )  and  mount  in  damar  (p.  38). 

No.  139. — The  Male  Urethra. — Treat  pieces  i  to  3  cm.  long  of  the 
prostatic,  membranous,  and  cavernous  portions  and  of  the  fossa  navicularis 
like  No.  138.  Care  should  be  exercised  not  to  confuse  the  lacuna;  of  Mor- 
gagni  (blind  evaginations  of  the  mucosa)  with  sections  of  glands. 


XV.  THE    TESTICLE   AND   THE    OVARY. 

No.  140. — For  a  general  view  of  the  testicle  make  a  transverse  incision 
through  the  testicle  and  epididymis  of  a  newborn  child  ;  fix  the  pieces  in  about 
50  c.c.  of  Kleinenl)erg's  picrosulphuric  acid  (p.  21)  and  harden  in  30  c.c. 
of  gradually  strengthened  alcohol  (p.  29).  Stain  thick  transverse  sections  of 
the  entire  organ  in  dilute  carmine  (p.  32),  and  in  Bohmer's  hematoxylin  (p. 
31),  and  mount  in  damar.  Examine  with  very  low  magnification  (Fig.  i86). 
In  the  testicle  of  the  rabbit,  cat,  and  dog  the  corpus  Highmori  is  not  at  the 
margin  but  in  the  center  of  the  organ.  If  no  incision  is  made  into  the  organ, 
it  does  not  harden  sufficiently,  because  the  dense  tunica  albuginea  retards  the 
penetration  of  the  fluids. 


312  HISTOLOGY. 

No.  141. — Minute  S/ructi/re  of  the  Seminiferous  Tubules. — Place  small  pieces 
(2  cm.  cubes)  of  the  fresh  testicle  of  an  ox  in  200  c.c.  of  Miiller's  fluid  (]). 
14),  and  after  14  days  harden  them  in  50  c.c.  of  gradually  strengthened  alco- 
hols. Cut  sections  as  thin  as  possible,  stain  them  in  Bohmer's  hematoxylin 
(p.  31),  and  mount  in  damar  (p.  38  ).  Even  with  the  low  power  tubules  in  a 
condition  of  activity  can  be  distinguished  from  resting  tubules  ;  the  former 
may  be  recognized  by  the  intensely  blue  heads  of  the  young  spermatozoa  (Fig. 
187). 

No.  142. — Still  better  preparations  maybe  obtained  by  placing  the  entire 
testicle  of  a  mouse  in  10  c.c.  of  the  platino-aceto-osmic  acid  mixture  (p.  21) 
for  24  hours  for  fixation,  then  washing  it  for  several  hours  in  running  water, 
and  hardening  it  in  20  c.  c.  of  gradually  strengthened  alcohols.  Mount 
the  unstained  sections  in  damar  (Fig.  18S).  The  platino-aceto-osmium  mix- 
ture does  not  penetrate  sufficiently  into  the  testicles  of  larger  animals,  which 
therefore  are  not  suitable. 

No.  143. — Elements  of  the   Testicle. — Place  pieces  about    i  cm.  in  size 
of  the   fresh  testicle  of  an  ox  in   20  c.c.  of  Ranvier's  alcohol   (p.  19)   and 
in  5  to  6  hours  tease  the  tubules  in  a  drop  of  the  same 
j1  alcohol.     Stain    under    the   cover-glass  with    picrocar- 

mine,  and  mount  in  dilute  glycerine.  Several  prepara- 
tions from  different  parts  of  the  organ  should  be  com- 
pleted, and  then  not  infrequently  the  cells  of  Sertoli 
with  attached  spermatocytes,  or  the  seminal  filaments 
Ijroduced  by  them,  will  be  obtained  (Fig.  268,  b). 

No.  144. — Elements  of  the  Semen. — Make  an  in- 
cision into  a  fresh   epididymis,  and  place  one  drop  of 
the  milk-white  fluid  that  exudes  from  the  cut  surface 
Fig.  268.— Tsolatbd   Ele-     on  a  clean  slide  ;  add  one  drop  of  salt  solution,  apply 
MBNTs  OP  Testicle  OP     a  cover-glass,  and  examine  with  the  hitrh  power.      After 

Ox.    X  240.    a,  c.  Mother-  .  ^  .  .^       t 

cells;  *,■•  spermatoblast;"     a  tmic  let  One  drop  of  distilled  water  flow  under  the 

m'ent"l"'?,'"matu'rT'"eminai     cover-glass ;    the  movements  of  the  spermatozoa   soon 

'"='""="'■  cease  ;  the  heads  of  the  majority  of  the  seminal  filaments 

then  present  their  broad  surface,  and  the  tail  curves  and 

forms  a  loop  (Fig.  189,  3).      Remnants  of  protoplasm  still  adhere  to  seminal 

filaments  not  fully  matured.     The  spermatozoa  may  be  preserved  by  allowing 

the  semen  diluted  with  water  to  dry  on  the  slide  ;  then  apply  a  cover-glass  and 

secure  it  with  cement   (p.   38).      In   examining  such  preparations,  too  much 

illumination  gives  rise  to  troublesome  reflections.      For  spiral   fibrils,  examine 

the  spermatozoa  of  the  rat  in  water ;  use  an  immersion  lens. 

No.  145. — The  vitality  of  the  seminal  filaments  has  led  to  investigations 
for  forensic  purposes.  It  may,  for  example,  be  a  question  as  to  whether  spots 
occurring  on  a  linen  garment  were  produced  by  semen.  Cut  strips  5  to  10  mm. 
long  from  the  suspected  spots,  soak  them  for  from  5  to  10  minutes  in  a  watch- 
glass  containing  distilled  water,  and  tease  a  few  fibers.  With  the  high  power 
(500  :  i)  examine  chiefly  the  edges  of  the  isolated  linen  fibers,  to  which  the 
seminal  filaments  if  present  are  attached.  Not  infrequently  the  heads  have  been 
broken  off;  they  are  recognized  by  their  peculiar  luster,  their  shape,  and  their 
(in  man  small)  size. 

No.  146. — Seminal  Filaments  of  the  Frog. — The  male  frog  is  recognized 
by  a  well-developed  wart  on  the  ball  of  the  thumbs.  Open  the  abdominal 
cavity  ;    the  testicles  are  a  pair  of  oval  bodies  (similar  to  the  kidneys  of  mam- 


SPECIAL    TKCHNIQUE.  313 

mals)  lying  to  either  side  of  the  vertebral  column.  Divide  the  organ  by  a 
transverse  incision  ;  dilute  a  drop  of  the  fluid  with  a  drop  of  salt  solution. 
The  seminal  filaments  are  large,  the  head  thin  and  elongated,  the  tail  so  deli- 
cate that  at  the  first  glance  it  may  be  overlooked.  Immature  filaments  lie 
grouped  in  tufts. 

No.  147. — Epiiiidyinis,  Vas  Deferens,  and  Seminal  I'esicles. — Pieces  i  to 
2  cm.  in  size  are  to  be  fi.xed  in  200  c.c.  of  Miiller's  fluid  and  in  14  days  hardened 
in  60  c.c.  of  gradually  strengthened  alcohol  (p.  29).  Stain  the  sections  with 
Bohmer's  hemato.vylin  and  mount  in  damar  (  Fig.  191  and  192). 

No.  148. — The  prostate  and  the  different  divisions  of  the  male  urethra  are 
to  be  prepared  in  2  to  3  cm.  cubes  like  Xo.  147  (  Fig.  193  ). 

No.  149. — The  Ovary. — The  ovaries  of  small  animals  may  be  fixed  in 
toto  and  those  of  larger  animals  with  several  incisions  transverse  to  the  long 
axis  in  100  to  200  c.c.  of  Kleinenberg's  picrosulphuric  acid  (p.  28),  and 
hardened  in  100  c.c.  of  gradually  strengthened  alcohol  Tp.  29).  For  a  topo- 
graphical view  (Fig.  194)  it  is  advisable  to  cut  thick  sections,  because  other- 
wise the  contents  of  the  follicles  easily  fall  out.  Not  every  section  includes 
large  follicles;  it  is  often  necessary  to  cut  many  sections  in  order  to  strike  a 
favorable  place.  Stain  the  sections  with  Bohmer's  hematoxylin,  or  in  bulk 
with  borax-carmine  (p.  32).      Mount  in  damar  (p.  38). 

No.  150. — Fresh  ora  may  be  obtained  as  follows  :  Procure  the  fresh  ovaries 
of  a  cow.  The  large  Graafian  follicles  are  transi)arent,  pea-sized  vesicles, 
which  with  scissors  may  be  easily  shelled  out  in  toto.  Transfer  the  isolated 
follicle  to  a  slide  and  prick  it  with  a  needle.  The  needle  must  be  thrust  in 
carefully  on  the  side  of  the  follicle  lying  against  the  slide,  otherwise  the  liquor 
will  spurt  out  and  carry  the  ovum  with  it.  ^\'ith  the  low  power,  and  without 
placing  a  cover-glass  on  the  preparation,  search  for  the  ovum,  which,  surrounded 
by  the  cells  of  the  cumulus  ovigerus,  will  be  found  in  the  escaping  licjuor  folliculi 
(Fig.  19S,  A).  Place  two  narrow  stri])s  of  paper  on  either  side  of  the  ovum, 
carefully  apply  a  cover-glass,  and  examine  with  the  high  power. 

Often  the  ovum  does  not  escape  when  the  follicle  is  pricked  ;  it  may  then 
be  found  by  teasing  the  follicle. 

No.  151. — Ova  of  the  Frog. — Place  a  small  jiiece  of  the  fresh  ovary  of  a 
frog  on  a  slide,  and  prick  all  the  large  pigmented  ova,  so  that  their  contents 
escape.  Place  that  which  remains  in  a  watch-gla.ss  with  distilled  water  and 
wash  it  by  moving  it  to  and  fro  with  needles.  Place  the  watch-glass  on  a 
black  background  ;  the  smaller,  still  unpigmented  follicles  can  then  be  seen. 
Transfer  the  washed  object  to  a  clean  slide,  apply  a  cover-glass,  and  examine 
it.  The  ova  have  very  large  germinal  vesicles  ;  the  germinal  spot  disappears 
early,  and  usually  is  not  to  be  seen.  On  the  other  hand,  a  dark  spot  occurs 
in  the  vitellus,  the  "  nucleus  of  the  vitelUis. "  Surrounding  the  ovum  is  a 
finely-striated  membrane,  the  inner  surface  of  which  is  covered  with  flat  cells  ; 
this  is  the  theca  folliculi  with  the  simple  follicular  epithelium. 

No.  152. — The  Oi-iditcts. — Pieces  i  to  2  cm.  long  are  to  be  fixed  in  50 
c.c.  of  3  per  cent,  nitric  acid,  and  after  5  hours  hardened  in  60  c.c.  of  gradually 
strengthened  alcohol.      Stain  with  Bohmer's  hematoxylin  and  mount  in  damar. 

No.  153.  —  The  Uterus. — -The  human  uterus  in  many  cases  is  not  suitable 
for  the  production  of  tojwgraphical  pre|>arations.  Insurmountable  difficulties 
are  often  encountered,  especially  in  rendering  the  gland-tubules  evident.  In 
the  two-horned  uterus  of  many  animals,  the  often  greatly-convoluted  follicles 


314  HISTOLOGY. 

may  be  more  readily  seen  ;  the  arrangement  of  the  muscular  strata  is  more 
regular,  and  dififerent  from  that  of  the  human  organ. 
The  specimens  are  to  be  prepared  like  No.  152. 


XVI.  THE  SKIN  AND  ITS  APPENDAGES. 

No.  154. — Strata  of  the  Skin;  Coil-glands. — Cut  from  the  pad  of  the 
finger,  from  the  palm  of  the  hand,  or  the  sole  of  the  foot,  pieces  of  skin  i  to  2 
cm.  square  together  with  a  thin  stratum  of  subjacent  fat  and  place  them  in 
30  c.c.  of  absolute  alcohol.  To  prevent  curling  of  the  pieces  pin  them  on  a 
small  cork-plate  with  the  epidermis  turned  toward  the  cork,  and  place  the  whole 
in  absolute  alcohol.  On  the  following  day  remove  the  pieces  from  the  cork- 
plate  and  place  them  for  from  3  to  4  weeks  in  50  c.c.  of  90  per  cent,  alcohol. 
Cut  thin  and  thick  sections.  The  latter  are  indispensable  in  order  to  see  the 
excretory  ducts  of  the  coil-glands  in  their  entire  length.  The  most  suitable  for 
this  purpose  is  the  skin  of  the  sole  of  the  foot  of  children,  because  the  ducts  of 
the  coil-glands  here  run  vertically  (Fig.  208).  Stain  with  alum  carmine,  10 
minutes  (p.  32)  ;  the  red  coils  can  be  seen  with  the  unaided  eye  ;  mount  in 
damar.  Examine  with  the  low  power.  In  thick  sections  the  papillae  are  often 
indistinct,  because  they  are  surrounded  by  the  red  colored  stratum  mucosum  ; 
the  screw-like  twisted  ends  of  the  excretory  ducts  may  be  most  distinctly  seen 
when  the  object  is  faintly  illuminated  or  with  obli(|ue  illumination  (see  p.  43, 
remark*).  To  render  the  stratum  granulosum  visilile,  bulk  staining  with  borax- 
carmine,  2  to  3  days  (p.  32),  is  to  be  recommended.  The  granules  of  this 
stratum  are  then  stained  an  intense  red. 

No.  155. — For  preparations  of  the  nails  fix  the  distal  phalanx  of  a 
child  8  to  12  years  of  age  (in  adults,  that  of  the  little  finger,  if  possible  of 
women),  2  to  4  weeks  in  100  to  200  c.c.  of  Miiller's  fluid,  and  harden  in  about 
100  c.c.  of  gradually  strengthened  alcohol  ;  decalcify  (p.  29)  ;  harden  again, 
and  stain  thick  cross-sections  10  minutes  in  alum  carmine  (p.  32).  In  cutting 
sections  place  the  knife  on  the  volar  side  (not  on  the  nail  side)  of  the  phalanx. 
The  substance  of  the  nail  frequently  shows  diflerently-colored  strata.  In  the 
nails  of  old  cadavers  the  epithelium  often  becomes  loosened  from  the  ridges. 

No.  156. — Elements  of  the  Nails. — Place  pieces  of  cut  nail  i  to  2  mm.  broad 
in  a  test-tube  containing  5  c.c.  of  concentrated  potash-lye  and  heat  over  a  flame 
until  it  boils  up  once.  Transfer  the  nail  with  a  drop  of  the  lye  to  a  slide  and 
scrape  off  some  of  the  softened  surface  ;  apply  a  cover-glass.  On  examination 
with  a  high  power,  cells  will  be  found  like  those  in  Fig.  211.  For  comparison, 
,  investigate  the  horny  cells  of  the  stratum  corneum,  which  may  be  obtained  by 
lightly  scraping  the  pad  of  the  finger  with  the  handle  of  a  scalpel.  Examine 
the  polygonal  scales  in  a  drop  of  distilled  water,  with  a  high  power. 

No.  157. — Hairs. — Place  a  hair  in  a  drop  of  salt  solution  on  a  slide  and 
examine  it  with  the  low  and  the  high  power  ;  the  most  suitable  for  study  are 
white  hairs  and  the  hairs  of  the  beard.  The  hair-cuticle  of  man  is  very  delicate 
and  the  transverse  markings  produced  by  the  imbrication  of  the  cells  are  often 
very  indistinct;  usually  only  fine  wavy  lines  are  visible.  The  hairs  of  many 
animals,  on  the  other  hand,  show  the  cuticula  very  well,  for  example,  sheep's  wool. 

No.  158. — For  the  demonstration  of  the  elements  of  the  hairs,  place  a 
piece  of  hair  i  to  2  cm.  long  in  a  drop  of  pure  sulphuric  acid  on  a  slide  and 
apply  a  cover-glass  ;  press  lightly  on  the  glass  with  a  needle  and  the  cortical 
substance  will  split    up  into  fibers,  which  consist  of  adherent  cortical  cells. 


SPECIAL    TECHNIgUE.  315 

Slightly  warm  the  slide,  press  again  with  a  needle,  so  that  the  cover-glass  becomes 
slightly  displaced  ;  numerous  free  elements,  superficial  scales,  and  cortical  cells 
will  then  be  seen. 

Xo.  159. — For  the  exhibition  of  the  elements  of  the  hair-follicles  (and  the 
hairs)  cut  from  a  mustachioed  human  upper  lip  a  piece  2  cm.  square  and  place  it 
in  dilute  acetic  acid  (5  c.c.  of  acetic  acid  to  100  c.c.  of  distilled  water).  In  2 
days  the  individual  hairs  with  their  sheaths  can  be  easily  withdrawn  and  their 
elements  separated  by  teasing  in  a  drop  of  distilled  water  (Fig.  213).  The 
cells  of  Henle's  sheath  float  in  small  complexes  in  the  prejjaration  and  closely 
resemble  fenestrated  membranes  (Fig.  213,  5).  Not  infrequently  a  hair-follicle 
is  obtained  at  the  base  of  which  anew  hair  is  developing  (compare  with  Fig.  126). 

No.  160. — For  the  study  of  hair  ami  hairfollicles  place  pieces  2  to  3 
cm.  square  of  the  fresh  skin  of  the  scalp  in  about  200  c.c.  of  a  2.5  per  cent, 
solution  of  pota.ssium  bichromate  (p.  20,  9)  for  from  4  to  8  weeks;  wash 
them  I  to  3  hours  in  running  water  and  harden  in  the  dark  in  about  100  c.c. 
of  gradually  strengthened  alcohol.  Longitudinal  sections  which  include  the 
entire  length  of  the  follicle  are  very  difficult  to  cut.  Macroscopic  orientation 
as  to  the  direction  of  the  hair  is  first  necessary.  To  obtain  preparations  like 
that  in  Fig.  212  thick  sections,  unstained,  are  to  be  mounted  in  glycerine.  Thin 
sections  usually  include  only  a  portion  of  the  hair-follicle.  It  is  much  easier  to 
cut  thin  cross-sections,  but  care  must  be  taken  to  make  the  cut  vertical  to  the 
longitudinal  direction  of  the  hair,  not  parallel  to  the  surface  of  the  skin.  In 
this  way  a  single  section  shows  different  levels  of  the  hairs  and  hair-follicles  ; 
such  sections  are  to  be  stained  in  dilute  carmine  (p.  32),  and  Bohmer's  hema- 
toxylin (p.  31),  or  better,  first  with  hematoxylin  and  then  with  picrocarmine 
(P-  33)  1°  minutes,  and  mounted  in  damar.  I-"specially  instructive  are  the 
sections  through  the  hair-follicle  close  to  the  hair-bulb  (Fig.  214). 

No.  161. — For  the  development  of  hair  cwi  pieces  about  2  cm.  scjuare  of 
the  skin  of  the  forehead  (not  of  the  hairy  scalp)  of  a  5-  to  6-months'-old 
human  embryo  ;  s[)an  them  out  (see  No.  154)  ;  ])lace  them  for  14  days  in  too  to 
200  c.c.  of  Miiller's  fluid  and  harden  in  about  100  c.c.  of  gradually  strengthened 
alcohol.  Stain  the  tissue  in  bulk  in  bora.\ -carmine  (p.  32).  The  sections 
may  also  be  stained  in  Bohmer's  hematoxylin  (p.  31).  Embed  the  tissue 
in  liver ;  endeavor  to  cut  sections  exactly  in  the  direction  of  the  hair-follicle, 
which  is  much  more  easily  done  than  in  the  hairy  scalp  of  the  adult.  Mount 
in  damar.  The  sections  exhibit  all  stages  of  development  (Fig.  215).  The 
epidermal  thickenings  are  only  to  be  seen  in  well-preserved  epidermis,  which 
in  embryos  is  often  somewhat  macerated.  They  are  more  easily  found  in  em- 
bryos of  the  lower  animals. 

No.  162. — Shedding  and  Replacement  of  Hair. — The  eyelids  of  new- 
born children  are  most  suitable.  Treat  like  No.  182,  Cut  sagittal  sections. 
Vertical  sections  of  the  hairy  scalp  often  yield  good  results  (Fig.  216). 

No.  163.  —  The  Sebaceous  Glands. — Fix  and  harden  the  alse  nasi  of  an 
infant  in  100  c.c.  of  2.5  per  cent,  solution  of  potassium  bichromate 
(like  No.  160).  Cut  thick  and  thin  sections  ;  stain  them  with  dilute  carmine 
(p.  32),  and  with  Bohmer's  hematoxylin  (p.  31),  and  mount  in  damar.  Sec- 
tions lengthwise  to  the  dorsum  of  the  nose  often  show  both  sebaceous 
glamls  and  hair-follicles,  but  they  must  be  made  exactly  vertical.  The  alK  of 
the  nose  of  adults,  on  account  of  the  very  large  sebaceous  glands  with  their 
wide  excretory  ducts,  do  not  furnish  good  microscopic  specimens.     Small  seba- 


3l6  HISTOLOGY. 

ceous  glands  with  hair-follicles  can  be  seen  with  the  unaided  eye  in  stripping 
off  the  macerated  epidermis  of  old  cadavers. 

No.  164. — Blood-Tcsseh  of  tlic  Skin. — Inject  with  Berlin  blue  the  entire 
hand  of  a  child  through  the  ulnar  artery  (or  a  foot  through  the  posterior  tibial 
artery)  and  place  it  in  i  to  2  liters  of  Miiller's  fluid  ;  after  several  days  cut 
pieces  2  to  3  cm.  square  of  the  palm  of  the  hand  or  of  the  sole  of  the  foot, 
place  them  (2  to  4  weeks)  in  100  to  200  c.c.  of  Miiller's  fluid  for  fi.xation, 
and  harden  them  in  100  c.c.  of  gradually  strengthened  alcohol.  Cut  thick 
sections  and  mount  them,  unstained,  in  damar.  The  papillfe  in  such  sections 
are  only  to  be  recognized  by  the  capillary  loops.  To  the  beginner  it  appears  as 
if  the  loops  extend  into  the  stratum  mucosum. 

No.  165. — For  a  general  view  of  f/w  maiininirv  g/aiitis  place  the  nipple 
and  a  portion  of  the  gland  (3  to  4  cm.  square)  in  60  to  100  c.c.  of  absolute 
alcohol.  If  possible,  obtain  the  glands  of  an  individual  that  was  pregnant  not 
too  long  a  time  before  ;  also  the  glands  of  virgins,  etc.  Make  vertical  sections 
through  the  nipple  and  in  any  direction  through  the  gland-substance,  and  stain 
them  with  Bohmer's  hematoxylin  ;  mount  in  damar. 

No.  166. — For  the  minute  structure  of  the  mammary  glands  place  the  warm 
living  tissue  (3  to  5  mm.  cubes)  of  a  pregnant  mammal  in  5  c.c.  of  Flemming's 
mixture  (p.  21),  and  harden  after  i  to  2  days  in  30  c.c.  of  gradually  strength- 
ened alcohol.  Cut  very  thin  sections,  stain  them  with  saffranin  (p.  32,  4),  and 
mount  in  damar  (Fig.  219).  The  structure  is  often  difficult  to  understand 
on  account  of  the  small  size  of  the  gland-cells  (in  the  rabbit). 

No.  167. — FJemen/s  of  Milk. — Put  a  drop  of  salt  solution  on  a  clean 
slide,  and  add  to  it  a  drop  of  milk.  The  milk  is  to  be  obtained  by  placing 
the  cover-glass  upon  the  nipple  and  then  pressing  out  a  drop.  Examine  with 
a  high  power  (Fig.  221). 

No.  168. — Eletnents  of  the  Colostrum. — Proceed  as  in  No.  167.  Be  careful 
to  avoid  pressure  on  cover-glass.  The  nuclei  of  the  colostrum  corpuscles  can 
rarely  be  distinctly  seen  without  further  treatment ;  on  the  addition  of  a  drop 
of  picrocarmine  they  appear  as  dull-red  spots. 

XVII.    THE  EYE  AND  ITS  APPENDAGES. 

No.  169. — Carefully  cut  the  fresh  eye-ball  out  of  the  optic  cavity,  and 
secure  as  much  as  possible  of  the  optic  nerve ;  then  with  the  scissors  cut  off 
the  attached  fat  and  muscle,  and  with  a  sharp  razor  make  an  incision  at  the 
equator,  about  i  cm.  long,  through  all  the  coats  of  the  eye.  Place  the  eye-ball 
in  150  c.c.  of  0.05  percent,  chromic  acid  solution  (p.  20)  ;  after  12  to  20 
hours,  beginning  at  the  incision  already  made,  divide  the  eye-ball  with  the 
scissors  completely  into  an  anterior  and  posterior  half,  and  change  the  fluid. 
After  12  to  20  hours  more,  wash  the  pieces  and  harden  them  in  100  c.c.  of 
gradually  strengthened  alcohol. 

a.  Carefully  remove  the  lens  from  the  anterior  half  of  the  eye-ball  and  treat 
it  further  like  No.  179  ;  then  cut  out  a  quadrant  and  with  the  attached  ciliary 
body  and  iris  embed  it  in  liver  and  cut  sections  thro\igh  tlie  iridocorneal  angle. 
The  thick  sections  are  to  be  stained  with  Bohmer's  hematoxylin  and  mounted 
in  damar  (Fig.  227). 

/'.  From  the  remaining  three-fourths  of  the  anterior  half  of  the  eye-ball 
cut  out  a  piece  of  the  cornea,  5  to  10  mm.  square,  embed  it  in  liver  and  make 
sections  through  the  layers  of  the  cornea  (Fig.  222  ).    The  alternating  lamellas  of 


SPECIAL    TECHN1(,)UE.  3I7 

the  substantia  propria  can  only  be  well  seen  in  unstained  sections  mounted  in 
dilute  glycerine. 

c.  From  the  posterior  half  of  the  eye-ball  cut  pieces  including  the  three 
coats,  5  to  10  mm.  square,  and  cut  sections,  not  too  thin,  for  the  study  of  the 
strata  of  the  sclera  and  choroid  {Y\%.  225).  Stain  them  with  Bohmer's  hema- 
to.\yiin  and  mount  in  damar.    In  sectioning,  the  retina  usually  becomes  loosened. 

(/.  For  i)reparations  showing  the  entrance  of  the  optic-nerve  cut  around  the 
point  of  entrance  at  a  distance  of  about  5  mm.  from  the  same  through  all  tiie 
coats  of  the  eye  ;  embed  this  jjortion  with  about  i  cm.  of  the  optic-nerve  in 
liver  and  cut  sections  (not  too  thin).  Place  the  knife  so  that  it  strikes  the 
retina  first,  then  the  choroid  and  sclera,  and  passes  through  the  optic-nerve 
longitudinally;  stain  with  dilute  carmine  (p.  32)  and  with  Bohmer's  hema- 
to.xylin  (p.  31),  and  mount  in  damar.  Examine  with  very  low  magnification 
(Fig.  235). 

No.  170. — Remove  a  fresh  eye-ball  according  to  the  method  given  in  No. 
169;  make  an  incision  at  the  eiiuator.  and  jilace  it  in  100  to  200  c.c.  of 
Miiller's  fluid.  In  12  to  20  hours  divide  it  with  the  scissors  into  an  anterior 
and  posterior  half  In  2  to  3  weeks  carefully  wash  both  halves  in  slowly 
running  water  for  from  i  to  2  hours.  Then  cut  pieces  including  all  the  coats, 
about  8  mm.  long,  and  use  for  them  the  following  i)reparations  : — 

a.  Teased  Preparation  of  the  Choroid. — Tease  and  mount  a  fragment  in 
a  drop  of  dilute  glycerine;  it  exhibits  large  blood-vessels,  the  ca|)illaries  of  the 
choriocapillaris,  branched  pigment-cells,  elastic  fibers,  sometimes  also  the 
gla.ssy  membrane;  the  "lattice-work  "  of  the  latter  is  only  partially  distinct. 
The  isolated  membranes  may  be  stained  with  Bohmer's  hematoxylin  and 
mounted  in  damar,  but  the  more  delicate  structures  are  thus  rendered  indistinct 
(Fig.  226). 

/'.  Elements  of  the  Retina. — Tease  a  small  piece  of  the  retina  in  a  drop 
of  Miiller's  fluid,  carefully,  with  needles.  Along  with  many  fragments  of 
the  elements,  a  few  more  or  less  well-preserved  parts  will  be  found.  Human 
eyes  have  very  large,  beautiful  cone-visual  cells,  while  those  of  many  mammals 
are  very  small  ;  wholly  unsuitable  in  this  respect  are  the  eyes  of  the  rabbit ; 
unfortunately,  human  eyes  are  usually  no  longer  in  a  sufficiently  fresh  condition 
when  the  investigation  is  made.  The  outer  segments  of  the  cones,  also  of  the 
rods,  are  extremely  delicate  and  rapidly  disintegrate  after  death,  falling  into 
transverse  plates  and  at  the  same  time  curving  like  a  shepherd's  crook.  Later 
they  disappear  entirely.  In  order  to  see  beautiful  cone-visual  cells,  examine, 
according  to  the  method  just  given,  the  eyes  of  fishes.  (See  furtiier  No.  171 
and  172.) 

c.  The  remaining  parts  of  the  eye-ball  are  to  be  transferred  from  the 
water  to  80  c.c.  of  gradually  strengthened  alcohol  for  hardening:  when  the 
hardening  is  com|)leted,  cut  out  the  iris,  embed  it  in  liver,  and  make 
meridional  sections;  stain  them  in  Bohmer's  hematoxylin  and  mount  in  damar 
(Fig.  228). 

(/.  Cut  out  a  portion  i  cm.  long  of  the  retina,  including  the  ora  serrata. 
which  is  macroscopically  visible  as  a  wavy  line,  embed  it  in  liver,  and  make 
meridional  sections;    stain   them   in  hematoxylin  and   mount  in  damar  (Fig. 

234)- 

e.  Treat  in  the  same  manner  a  |)iece  of  tjie  retina  taken  from  the  posterior 
portion  of  the  eye,  where  the  optic-fiber  stratum  is  thickest.  The  radial  fibers 
of  Miiller  can  only  be  seen  in  their  entire  length  in  accurate  vertical  sections 
(Fig.  229  and  Fig.  230). 

f.    In  the  same  manner  treat   meridional  sections  through  the  macula  and 


3l8  HISTOLOGY. 

fovea.  It  is  not  difficult  to  cut  sections  of  the  macula,  but  on  the  other  hand 
very  difficult  to  obtain  satisfactory  sections  through  the  extremely  delicate  fovea. 
The  retina  should  not  be  loosened  from  the  choroid,  but  the  two  should  be 
sectioned  together.  (Among  the  lower  mannnals  only  the  ape  pcssesses  a  yellow 
macula  and  a  central  fovea ;  on  the  other  hand,  the  majority — insectivora  and 
certain  rodents  excepted — have  an  "  area  centralis,"  without  yellow  pigmenta- 
tion, but  similar  in  structure  to  the  macula.  A  simple  or  multiple  fovea  is  always 
present  in  birds  and  reptiles ;   a  fovea  has  also  been  found  in  bony  fishes. ) 

No.  171. — Fresh  Elements  of  the  Retina. — Select  the  warm  eyes  of  animals 
lust  killed.  Divide  the  eye-ball  at  the  equator  and  carefully  remove  the  vitreous 
body  from  the  posterior  half;  cut  small  pieces  about  3  mm.  square  from  the 
transparent  retina  and  tease  in  a  drop  of  the  vitreous  humor;  place  two  thin 
strips  of  paper  on  either  side  of  the  preparation  (p.  41),  and  apply  a  cover- 
glass.  Isolated  elements  will  be  found  only  here  and  there  ;  on  the  other  hand, 
very  good  surface  views  are  not  infrequently  obtained  in  which  the  rods  and 
cones  are  perceptible  in  optical  cross-section,  the  first  as  small,  the  latter  as 
large  circles.  If  at  the  same  time  a  little  piece  of  the  pigmented  epithelium 
has  been  transferred  to  the  slide,  the  regular  hexagonal  cells  of  the  same  can 
be  plainly  seen  with  the  low  power.  The  light  spots  in  these  cells  are 
their  nuclei  (Fig.  8).  These  cells  are  also  very  unstable  and  soon  lose  their 
sharp  contours ;  molecular  motion  of  the  pigment-granules  may  be  very  fre- 
quently observed. 

No.  172. — -The  best  method  for  isolating  the  elements  of  the  retina  is  the 
following  :  Place  the  eye  unopened,  but  freed  from  fat  and  muscle,  in  i  per 
cent,  osmium  solution.  In  24  hours  cut  the  eye  open  at  the  equator  and  place 
it  for  maceration  for  2  to  3  days  in  distilled  water ;  then  with  scissors  cut  out  a 
piece  of  the  retina  about  2  mm.  long  and  tease  it  in  a  drop  of  water  ;  the  prep- 
aration may  be  stained  with  picrocarmine,  under  the  cover-glass,  and  mounted 
in  dilute  glycerine.  With  the  high  power,  in  addition  to  many  fragments  whose 
source  is  not  always  to  be  determined  with  certainty,  elements  like  those  pic- 
tured in  Fig.  232  may  be  found. 

It  is  advisable  to  select  the  eyes  of  small  animals — e.  g.,  a  small  salaman- 
der (Triton  tasniatus),  whose  sclera  is  thin  and  allows  the  osmium  solution  to 
penetrate  easily.  For  such  an  eye  i  to  2  c.c.  of  the  solution  will  be  sufficient. 
The  form  of  the  rods  is  quite  different  from  those  of  mammals ;  they  are  thick 
and  are  provided  with  long  outer  segments ;  the  cones  are  small. 

No.  173. — Corneal  Spaces  and  Canaliculi. — Select  an  eye  as  fresh  as  pos- 
sible ;  of  the  eyes  of  animals,  that  of  the  ox  is  most  suitable  ;  with  the  handle 
of  a  scalpel  scrape  away  the  epithelium  of  the  cornea  ;  spray  the  denuded  sur- 
face with  distilled  water  ;  cut  the  eye  through  in  front  of  the  attachment  of 
the  ocular  muscles  and  place  the  anterior  segment,  containing  the  entire  cornea, 
down  on  the  epithelial  side  ;  then  with  forceps  and  scalpel  remove  the  ciliary 
body,  the  lens,  and  the  iris,  so  that  only  the  anterior  portion  of  the  sclera  and 
cornea  remain,  which  are  to  be  placed  in  40  c.c.  of  a  i  per  cent,  solution  of 
silver  nitrate.  The  whole  is  then  to  .be  placed  in  the  dark,  3  to  6  hours,  and 
then  transferred  to  50  c.c.  of  distilled  water  and  exposed  to  sunlight  (see  further 
p.  35).  Harden  the  objects  in  50  c.c.  of  gradually  strengthened  alcohol  and  cut 
horizontal  sections,  which  is  most  easily  done  if  the  cornea  is  held  over  the  left 
index-finger.  It  is  best  to  take  the  sections  on  the  posterior  surface  of  the 
cornea,  since  the  spaces  and  canaliculi  are  more  regular  there.  The  sections 
may  be  stained  in  Bohmer's  hematoxylin  and  mounted  in  damar.  The  pic- 
tures are  negative,  the  spaces  and  canaliculi  white  on  a  brown  or  brown-yellow 


SPECIAL    TECHNIQUE.  319 

surface  (Fig.  223).  Examine  carefully  the  usually  somewhat  thinner  margins 
of  the  section  ;  in  sections  stained  in  hematoxylin  the  nuclei  of  the  fixed  cor- 
neal corpuscles  are  a  dull  blue  ;  the  contours  of  the  cells  can  seldom  be  per- 
ceived. 

No.  174. — Fixed  Corneal  Corpuscles  by  the  Gold  Method. — The  method 
described  on  p.  35  is  to  be  somewhat  modified,  as  follows  :  Express  the  juice 
from  a  fresh  lemon  ;  filter  it  through  flannel.  Kill  the  animal,  cut  out  the 
cornea  and  place  it  for  5  minutes  in  the  lemon-juice,  in  which  it  becomes  trans- 
jjarent  ;  then  wash  it  in  5  c.c.  of  distilled  water  for  i  minute;  transfer  it  to 
10  c.c.  of  gold-chloride  solution  and  place  it  in  the  dark  for  15  minutes. 
With  glass  rods  transfer  the  cornea  to  10  c.c.  of  distilled  water  for  i  minute, 
then  to  50  c.c.  of  distilled  water  to  which  2  drops  of  acetic  acid  have  been 
added,  and  expose  it  to  daylight ;  in  24  to  48  hours  the  reduction  is  completed. 
The  object  is  then  to  be  placed  in  10  c.c.  of  70  per  cent,  alcohol  (in  the 
dark)  ;  on  the  following  day  cut  out  a  little  piece  of  the  cornea,  hold  it  with 
needle  and  scalpel  at  the  edges  and  sejiarate  the  thin  lamella  from  the  posterior 
surface ;  this  can  be  done  successfully  without  much  trouble.  Mount  the 
lamellae  in  damar.  In  frogs  the  canaliculi  are  very  regular  and  the  posterior 
lamellae  easy  to  strip  off. 

No.  175. — Very  good  preparations  oi  fixed  corneal  cells  are  obtained  by 
the  method  of  Drasch.  The  objects  are  not  to  be  taken  from  the  animal  re- 
cently killed,  but  12  to  24  hours  after  death,  during  which  time  the  cadaver 
must  be  kept  in  a  cool  place.  Small  pieces  of  the  cornea  are  to  be  cut  out, 
about  6  mm.  long,  placed  in  5  c.c.  of  1  per  cent,  gold-chloride  solution  plus 
5  c.c.  of  distilled  water  and  stood  in  the  dark  for  i  hour.  During  this  time 
stir  the  fluid  often  with  a  gla.ss  rod  ;  then  with  glass  rods  transfer  the  pieces  to 
30  c.c.  of  distilled  water,  in  which  they  should  remain  (in  the  dark)  8  to  16 
hours.  They  are  then  to  be  transferred  to  25  c.c.  of  distilled  water  plus  5 
c.c.  of  formic  acid  and  exposed  to  daylight.  When  the  reduction  is  completed 
(p.  35)  the  dark-violet  pieces  are  to  be  hardened  in  gradually  strengthened 
alcohol,  and  in  about  6  days  thin  sections,  parallel  to  the  surface,  can  be  cut 
and  mounted  in  damar  (Fig.  224). 

No.  176. — Nen'es  and  Blood-vessels  of  the  Fresh  Cornea. — Select  the  eye 
of  an  ox  and  cut  out  the  cornea  and  the  portion  extending  from  the  limbus 
to  the  attachment  of  the  ocular  muscles;  remove,  with  scalpel  and  forceps,  the 
ciliary  body,  iris,  and  lens,  cut  out  a  quadrant  of  the  cornea,  place  it  with  the 
epithelial  side  up  on  a  slide,  and  apply  a  cover-glass  ;  a  drop  of  the  vitreous 
humor  may  be  added.  The  very  thick  preparation  must  be  examined  with  a 
low  ])ower.  .\t  the  scleral  margin  the  loops  formed  by  the  blood-vessels  as 
they  bend  back  can  be  seen  when  the  surface  of  the  cornea  is  in  focus  ;  the 
most  of  them  still  contain  blood-corpuscles.  Medullated  nerve-fibers  are  also 
found  here,  as  well  as  in  the  deeper  strata  ;  they  are  arranged  in  bundles  and 
within  the  cornea  can  only  be  traced  for  a  short  distance.  The  elongated 
pigment-streaks  found  in  the  eye  of  the  ox  have  no  relation  to  the  nerves. 

This  method  is  not  serviceable  for  the  exhibition  of  the  finer  distribution 
of  the  nerves. 

No.  177. — Nerves  of  the  Cornea. — a.  Gold  Method. — Cut  out  the  cornea 
I  2  to  24  hours  after  death,  remove  the  ciliary  body  and  iris,  and  treat  it  accord- 
ing to  the  method  given  in  No.  175.  When  the  hardening  is  completed  cut 
horizontal  sections,  which  contain  the  epithelium  and  the  uppermost  strata  of  the 
cornea,  and  vertical  sections  through  the  thickness  of  the  cornea.  Mount  in 
damar  (Fig.  239). 


320  HISTOLOGY. 

b.  Methylene  Blue  Staining. — Kill  a  rabbit;  remove  the  entire  eye-ball; 
free  it  from  the  attached  remnants  of  ocular  muscles  and  connective-tissue  ; 
place  it  in  a  watch-glass  and  with  a  sharp  scalpel  make  a  deep  incision  through 
all  the  coats  of  the  eye  at  the  equator.  The  vitreous  humor  thus  escapes  into 
the  watch-gla.ss  ;  then  with  scissors  separate,  at  the  incision,  the  entire  cornea, 
place  it  on  a  slide  with  the  concave  surface  upward,  and  scrape  off  with  the 
handle  of  the  scalpel  the  ciliary  body,  iris,  and  lens,  which  is  easily  done  ; 
transfer  the  cornea  thus  cleansed  to  a  second  watch-glass  containing  3  to  lo 
drops  of  the  vitreous  humor  and  3  to  4  drops  of  a  J^  per  cent,  methylene  blue 
solution.     The  fluid  must  cover  the  concave  surface  of  the  cornea. 

The  time  required  for  staining  cannot  be  given  with  certainty  ;  it  is  there- 
fore advisable  after  several  hours  to  place  the  cornea  with  the  convex  surface  up 
on  a  clean  slide  and,  without  a  cover-glass,  to  examine  it  with  the  low  power  ; 
if  it  is  not  sufficiently  stained  return  it  to  the  watch-glass  and  examine  it  again 
in  about  10  minutes. 

So  soon  as  the  nerves  can  be  distinctly  seen  the  cornea  is  to  be  transferred 
for  from  18  to  20  hours  to  20  c.c.  of  ammonia;  then  cut  out  a  quadrant  and 
mount  it  in  dilute  glycerine,  to  which  a  drop  of  ammonia  has  been  added  ; 
after  being  kept  for  24  hours  in  the  dark  the  preparation  will  be  sufficiently 
transparent  and  can  be  investigated  with  the  high  power. 

No.  I  78. —  Lens-fibers. —  Cut  the  eye-ball  open  back  of  the  equator; 
remove  the  vitreous  body  and  lens ;  thus  the  pigment  covering  the  ciliary 
processes  remains  attached  to  the  margin  of  the  lens.  Loosen  the  lens  from 
the  vitreous  body  and  place  it  in  50  c.c.  of  Ranvier's  alcohol  (p.  19).  In 
about  2  hours  thrust  needles  into  the  anterior  and  posterior  surfaces  of  the  lens 
and  strip  the  capsule  up  from  a  small  area  ;  this  is  easily  done  ;  if  lens-fibers 
are  attached  to  the  capsule  it  does  not  matter.  On  pricking  the  lens  a  turbid 
white  fluid  escapes;  shake  the  alcohol  and  let  the  lens  remain  in  it  10  to  40 
hours.  .\t  the  expiration  of  this  time  the  lens  can  be  easily  separated  into 
shell-like  pieces.  Tease  a  small  strip  of  one  of  these  pieces  in  a  small  drop  of 
salt  solution  on  a  slide  (p.  25).  Apply  a  cover-glass,  taking  care  to  avoid 
pressure ;  if  it  is  desired  to  preserve  the  fibers,  stain  with  picrocarmine 
(staining  usually  occurs  in  a  few  minutes),  and  mount  in  dilute  acidulated 
glycerine  (Fig.  236,  A). 

No.  179. — Lens-fibers  in  Transverse  Section. — Place  a  lens  in  50  c.c.  of 
0.05  per  cent,  chromic  acid.  A  cloth  or  a  little  cotton  must  be  placed  on  the 
bottom  of  the  bottle  or  the  lens  will  adhere  to  the  glass  and  burst.  This  may 
also  be  prevented  by  frequently  shaking  the  bottle.  In  24  to  48  hours  break 
up  the  lens  into  shell-like  pieces  with  a  needle,  transfer  them  after  10  to  15 
hours  to  30  c.c.  of  70  per  cent,  alcohol,  which  is  to  be  replaced  on  the  fol- 
lowing day  by  an  equal  quantity  of  90  per  cent,  alcohol.  With  the  scissors 
cut  the  pieces  through  in  the  region  of  the  equator,  and  so  embed  them  in  liver 
that  the  first  sections  shall  pass  through  the  zone  lying  next  to  the  equator.  If 
the  section,  which  need  not  be  very  thin,  has  passed  through  the  fibers  trans- 
versely they  will  appear  as  sharply-defined  hexagons  ;  if,  on  the  contrary,  the 
section  is  oblique,  the  single  fibers  will  appear  to  be  separated  from  one  another 
by  irregular  zigzag  lines  ;  they  may  even  be  cut  partially  lengthwise.  The 
sections  are  to  be  transferred  directly  from  the  blade  to  the  slide  and  mounted 
in  dilute  glycerine  (Fig.  236,  £). 

No.  180. — The  Lens  Capsule  and  t/ie  Lens  Epithelium. — Place  the  eye- 
ball, free  from  muscle  and  fat,  in  100  to  200  c.c.  of  Miiller's  fluid.  Treat  it 
further  as  follows  :  — 


SPECIAL    TECHNIQUE.  32I 

</.  Surface  View  of  the  Lens  Capsule  and  Epithelium. — After  2  to  3  days 
cut  the  eye  open,  remove  the  lens,  and  with  forceps  strip  off  a  piece  of 
the  anterior  lens  capsule  ;  place  it  for  about  5  minutes  in  a  watch-glass  with 
distilled  water,  which  is  to  be  changed  once,  and  then  stain  it  in  Bohmer's 
hematoxylin  ;  mount  in  damar.  The  capsule  appears  a  homogeneous  light 
blue:  the  nuclei  and  the  contour  of  the  epithelial  cells  are  very  shar])  ( Fig. 
-2>liC  )■  If  it  is  desired  to  obtain  the  lens  capsule  alone  strip  off  a  portion  of 
the  posterior  lens  capsule. 

/'.  Sections  of  the  Capsule  and  Epithelium. — Let  the  eye-ball  remain  in 
iMiiller's  fluid  for  2  weeks ;  remove  the  lens,  wash  it  for  i  hour  in  running 
water  and  harden  it  in  50  c.c.  of  gradually  strengthened  alcohol  (p.  29)  ;  cut 
meridional  sections  through  the  anterior  surface  and  the  equator  of  the  lens ; 
stain   them   with    Bohmer's  hematoxvlin  (p.  31  )  and   mount   in   damar  (Fig. 

No.  181. —  The  Blood-vessels  of  the  Eye. — For  this  purpose  surface  prep- 
arations are  especially  suitable.  Open  a  fresh  eye  at  the  equator.  The  course 
of  the  central  artery  of  the  retina  is  macroscopically  perceptible.  For  the 
exhibition  of  the  blood-vessels  of  the  choroid  place  an  eyeball  completely 
freed  from  attached  muscle  and  fat  on  a  small  glass  funnel  which  has  been 
thrust  into  a  low  glass  bottle,  and,  with  scissors  and  forceps,  begin  at  the  eijua- 
tor  and  carefully  dissect  off  the  sclera.  With  a  little  practice  the  entire  sclera 
can  be  removed  beyond  the  ora  serrata  up  to  the  optic  entrance  without  injury 
to  the  choroid  ;  care  must  be  taken  not  to  tear  it.  (Beginners  should  be  con- 
tent to  remove  only  one  quadrant  of  the  sclera.)  All  the  firmer  points  of 
attachment  between  the  sclera  and  choroid  (the  venaj  vorticosre)  must  be  cut 
through.  Then  by  careful  brushing  with  a  sable  pencil  moistened  in  water 
remove  the  attached  portions  of  the  lamina  suprachoroidea  from  the  choroid  ; 
by  this  manipulation  the  course  of  the  larger  blood-vessels  is  brought  to  view. 
Thus  far  the  investigation  may  be  pursued  on  the  uninjected  eye  (compare  with 
No.  170,  a).  For  the  study  of  the  blood-vessels  of  the  ciliary  body  and  the 
iris  it  is  necessary  to  use  an  injected  eye,  divided  anterior  to  the  equator,  fixed 
in  Miiller's  fluid  and  hardened  in  alcohol.  The  iris  and  ciliary  body  may 
be  easily  stripped  from  the  sclera  ;  remove  the  lens  and  mount  in  damar. 
E,\amine  first  with  the  low  power. 

No.  182. — Place  the  upper  eyelid  oi  a  child  in  100  c.c.  of  0.5  per  cent, 
chromic  acid,  i  to  3  days,  wash  it  2  hours  in  running  water,  and  harden  in  50  c.c. 
of  gradually  strengthened  alcohol.  For  a  general  view  cut  thick  (F"ig.  240), 
for  the  finer  details  thin  sections  (Fig.  22,  C).  Staining  with  Bohmer's  hema- 
toxylin is  at  first  difficult,  l)ut  more  readily  accomplished  after  the  object  has 
lain  in  alcohol  several  months  (compare  p.  31,  remark*).      Mount  in  damar. 

No.  183.  —  The  Lacrymal  Glands. — The  lower  tear-gland  m  man  can  be 
easily  removed,  without  visible  external  injury,  from  the  fornix  of  the  conjunc- 
tiva. In  the  rabbit  this  gland  is  very  small  and  when  fresh  resembles  pale 
muscle  tissue.  It  must  not  be  confiised  with  Harder's  gland  lying  in  the 
median  angle  of  the  eye.  Treat  like  No.  112.  Small  pieces  i  mm.  square 
can  be  used.  The  excretory  duct  and  tubules  may  be  easily  seen  ;  difficult,  on 
the  other  hand,  it  is  to  see  the  intercalated  tulniles,  whose  epithelium  differs 
greatly  in  height  and  occasionally  is  so  low  that  care  must  be  taken  not  to  con- 
fuse tliem  with  blood-vessels. 


32  2  HISTOLOGY. 


XVIII.  THE  ORG.W  OF  HEARING. 

A  fundamental  condition  is  an  exact  knowledge  of  the  macroscopic  an- 
atomy of  the  labyrinth.  The  difficulties,  the  failures,  depend  in  the  main  on 
inaccurate  knowledge  of  the  bony  labyrinth.  As  a  preliminary  all  parts 
lying  lateral  to  the  promontory  (os  tympanicum  and  ossicles  of  the  ear)  must 
be  removed,  so  that  this  is  distinctly  visible. 

No.  184. — Otoliths. — Chisel  out  the  promontory,  beginning  at  the  upper 
margin  of  the  fenestra  stapedii,  to  the  lower  margin  of  the  fenestra  rotunda. 
Then,  especially  if  the  bone  has  been  placed  in  water,  the  white  spots  (maculje) 
in  the  sacculus  and  utriculus  can  be  detected.  With  delicate  forceps  lift  out 
the  sacculus  and  spread  out  a  small  piece  in  diluted  glycerine  on  a  slide.  The 
otoliths  are  present  in  large  numbers,  but  are  very  small,  so  that  their  shape 
can  only  be  distinctly  seen  with  the  high  power  (  240  diameters).  The  gly- 
cerine must  not  be  too  thick,  or  it  will  render  the  otoliths  completely  invisible 
(Fig.  242). 

In  taking  out  the  saccules  portions  of  the  semicircular  canals  not  infre- 
quently may  be  removed  ;  stain  these  with  picrocarmine  and  mount  them  in 
dilute  glycerine.  Only  the  epithelium,  and  here  and  there  in  optical  section 
the  delicate  glassy  membrane,  can  be  seen.     The  connective  tissue  is  scanty. 

No.  1 85.  —  The  Cochlea. — The  base  of  the  cochlea  lies  in  the  bottom  of 
the  internal  auditory  meatus,  the  apex  is  directed  toward  the  Eustachian  tube, 
and  therefore  the  axis  of  the  cochlea  is  horizontal  and  trans\-erse  to  the  long 
axis  of  the  petrous  bone. 

Open  the  free  portion  of  the  cochlea,  that  is,  remove  the  promontory  close 
to  the  fenestra  rotunda,  open  the  apex  of  the  cochlea  and,  having  removed  the 
superfluous  osseous  mass  as  far  as  practicable,  place  the  ])reparation  in  20  c.c.  of 
0.5  percent,  osmicacid  (5  c  .c.  of  2  per  cent,  osmic  acid  to  15  c.c.  of  distilled 
water).  In  12  to  20  hours  wash  the  preparation  for  about  i  hour,  and  then 
place  it  in  200  c.c.  of  Miiller's  fluid.  In  3  to  20  days  (or  later)  open  up  the 
cochlea  and  examine  it  in  water.  The  osseous  spiral  lamina  can  be  seen  as  a 
delicate  lamella,  the  membranous  spiral  lamina  as  a  delicate  membrane, 
attached  to  the  axis  of  the  cochlea;  with  fine  forceps  break  off  pieces  of  the 
osseous  spiral  lamina;  do  not  lift  them  with  the  forceps,  but  carefully  with 
needle  and  section-lifter  remove  them  from  the  fluid  and  transfer  them  to  a 
drop  of  dilute  glycerine  on  a  slide.  It  is  advisable  to  break  off  the  axial  por- 
tion of  the  spiral  lamina  on  the  slide  with  needles,  because  the  relatively  thick 
osseous  process  renders  it  difficult  to  apply  a  cover-glass.  The  vestibular  sur- 
face must  be  directed  upward  ;  it  may  be  recognized  by  the  auditory  teeth, 
which  are  visible  when  the  upper  surface  is  in  focus  (Fig.  244),  while  the 
other  portions  are  not  distinct  until  the  tube  is  depressed  and  the  lower  planes 
are  focused.  With  the  low  power  only  the  interstices  of  the  auditory  teeth 
are  at  first  visible,  as  dark  lines  (Fig.  246);  the  papilte  likewise  cannot  be 
seen  immediately,  even  with  the  high  power,  but  become  distinct  after  the 
second  or  third  day.  The  chief  difficulty  lies  not  in  the  finishing,  but  in  the 
proper  examination  of  the  object ;  the  picture  alters  with  the  slightest  change 
in  focus.  In  Fig.  247,  B,  the  membranous  sjjiral  lamina  is  drawn  schemati- 
cally, as  seen  with  the  upper  surface  in  focus,  and,  therefore,  only  the  free  sur- 
face of  the  structure,  drawn  as  seen  from  the  side  in  A,  is  visible.  It  is  clear 
that  in  depressing  the  tube  the  head-plates  of  the  pillar-cells  are  no  longer 
visible,  but  their  bodies  (as  circles  in  optical  section)  ;  the  reticular  membrane, 


SPECIAL   TECHNIQUE.  323 

likewise,  disappears,  and  can  only  be  seen  when  the  tube  is  elevated.  The 
jjreparation  may  be  stained  with  picrocarmine  and  preserved  in  dilute  glycerine. 
The  foregoing  directions  are  intended  to  apply  to  the  human  ear  and  that  of 
the  cat.     The  labyrinths  of  children  are  to  be  recommended. 

Xo.  186. — Sections  of  the  Bony  and  Membranous  Cochlea. — Remove  the 
cochlea  of  a  child  from  the  labyrinth.  The  compact  osseous  substance  of  the 
cochlea  is  surrounded  by  spongy  bone  so  soft  that  the  latter  may  be  removed 
with  a  stout  penknife.  With  a  chisel  make  small  openings  in  the  cochlea  at 
two  or  three  places,  about  i  mm.  square,  in  order  to  facilitate  the  penetration 
of  the  fixation  fluid  ;  then  place  it  in  15  c.c.  of  distilled  water  plus  5  c.c.  of 
2  per  cent,  osmic  acid.  After  24  hours  remove  the  object,  wash  it  for  a  quarter 
of  an  hour  in  running  water,  and  harden  it  in  about  60  c.c.  of  gradually 
strengthened  alcohol.  When  the  hardening  is  completed,  decalcify  the  cochlea 
in  the  following  mixture  :  i  c.c.  of  a  i  percent,  aqueous  solution  of  ])alladium 
chloride,  lo  c.c.  of  hydrochloric  acid,  and  100  c.c.  of  distilled  water.  Place 
the  cochlea  in  100  c.c.  of  this  mixture,  which  must  be  changed  often.  When  the 
decalcification  is  completed,  the  object  should  be  hardened  again,  embedded  in 
liver,  and  sectioned.  The  sections  must  be  made  in  the  long  axis  of  the  cochlea. 
Stain  them  with  picrocarmine;  mount  in  damar.  It  is  not  difficult  to  obtain 
preparations  furnishing  a  good  general  view ;  the  vestibular  membrane  is 
usually  torn,  so  that  the  ductus  cochlearis  and  .scala  vestibuli  appear  as  a  com- 
mon space  (Fig.  243).  The  organ  of  Corti  leaves  most  to  be  desired  ;  only 
very  thin  sections  which  pa.ss  through  the  organ  vertically  furnish  intelligible 
jiictures  ;  usually  a  section  contains  several  inner  and  outer  pillar-cells,  also 
fragments  of  them  ;  the  cells  of  Hensen  appear  pale  and  swollen-  (Fig.  249)  ; 
orientation  presents  many  difficulties  to  the  beginner. 

.\niong  animals,  the  cochlea  of  the  guinea-pig  and  of  the  bat  are  to  be  recom- 
mended ;  it  is  not  embedded  in  spongy  bone  and  does  not  need  to  be 
chiselled  out  and  punctured,  but  can  be  placed  at  once  in  the  fixing  fluid. 

Xo.  187.  —  The  Nerves  of  the  Maciilce,  Cristie,  and  Cochlea. — For  this 
purpo.se  the  ear  of  the  newborn  mouse  is  recommended,  treated  according  to 
the  method  given  on  p.  35.  The  base  of  the  cranium,  after  removal  of  the 
vertex,  the  brain,  and  lower  jaw,  is  to  be  placed  for  from  3  to  4  days  in  the  osmio- 
bichromate  mixture  and  for  2  days  in  the  silver  solution.  As  a  rule  it  is 
necessary  to  employ  the  double  method  (p.  36).  Cut  horizontal  and  frontal 
sections  through  the  cranium,  without  decalcifying  it.  The  former  are  the 
more  readily  made. 

Xo.  188. — The  Eustachian  Tube. — To  obtain  transverse  sections  (includ- 
ing cartilage  and  mucosa)  the  oblique  direction  of  the  tube  downward,  for- 
ward, and  inward  must  be  ascertained.  Cut  out  the  ])haryngeal  division  of 
the  tube  together  with  the  surrounding  muscles  and  fix  it  in  200  to  300 c.c. 
of  Miiller's  fluid  (p.  27).  In  3  to  6  weeks  wash  it  in  running  water  and 
harden  it  in  100  c.c.  of  gradually  strengthened  alcohol  (p.  29).  The  sections 
may  be  stained  in  Bohmer's  hematoxylin  (p.  31)  and  mounted  in  daniar  (p. 
38).     For  a  general  view,  examine  with  the  low  power. 

No.  189.  —  The  Ceruminous  G/ands. — Cut  out  the  ear  with  the  cartilagin- 
ous auditory  passage  close  t6  the  bony  auditory  passage.  From  the  carti- 
laginous ])ortion  cut  a  jjiece  i  cm.  square  and  ])lace  it  in  30  c.c.  of  absolute 
alcohol.  The  tissue  may  be  sectioned  on  the  following  day.  If  it  is  desired 
to  see  the  coil  and  the  excretory  duct  the  sections  must  be  tolerably  thick 
( — 0.5  mm.).  Nuclear  staining  with  Bohmer's  hematoxylin  (p.  32)  may  be  em- 
ployed (Fig.  250).     Examine  thin  unstained  sections  in  diluted  glycerine  ;  in 


324  HISTOLOGY. 

these  the  fat-globules  and  pigment-granules  can  be  seen.  The  organs  of  new- 
born children  are  especially  suitable  for  this  purpose.  In  adults  the 
tubules  are  widely  dilated  and  do  not  furnish  good  general  views.  On  the 
other  hand,  the  cuticular  border  of  the  gland-cells  is  distinct  in  the  adult, 
which  in  the  newborn  I  miss  (compare  with  Fig.  251). 


XIX.  THE  MUCOUS  MEMBRANE  OF  THE  NOSE. 

Xo.  190.  —  Olfactory  Cells. — Saw  open  the  head  of  a  rabbit  in  the  median 
line.  The  olfactory  mucosa  is  easily  recognized  by  its  brown  color.  With  fine 
scissors  cut  out  a  small  piece,  about  5  mm.  long,  of  the  nuicosa,  together  with  the 
corresponding  portion  of  the  turbinal  bone,  and  place  it  in  20  c.c.  of  Ranvier's 
alcohol  (p.  19).  In  5  to  7  hours  transfer  the  same  to  5  c.c.  of  picrocarmineand 
on  the  following  day  to  10  c.c.  of  distilled  water.  In  about  10  minutes  remove 
the  piece  and  lightly  strike  it  against  a  slide  on  which  a  drop  of  diluted  glycerine 
has  been  placed  ;  stirring  with  the  needle  is  to  be  avoided.  Carefully  apply  a 
cover-glass.  In  addition  to  many  fragments  of  cells  many  well-])reserved  sus- 
tentacular  elements  may  be  obtained.  Very  frequently  the  delicate  central 
process  of  the  olfactory  cells  is  wanting  (Fig.  253). 

No.  191. — The  Miuoiis  Membrane  of  the  Respiratory  Region.- — Cut  out  a 
small  piece,  about  5  to  10  mm.  long,  from  the  lower  half  of  the  nasal  septum; 
strip  off  the  mucosa  and  fi.x  and  harden  it  in  about  20  c.c.  of  absolute 
alcohol  (p.  27).  Use  the  nasal  mucous  membrane  of  the  rabbit's  head  (No. 
190)  for  thin  sections  ;  embed  the  pieces  in  liver  (p.  31),  and  stain  sections 
with  Bohmer's  hemato.xylin  ;  mount  in  damar.  For  general  views  the  mucous 
membrane  of  human  cadavers  answers,  which  is  to  be  treated  in  the  same 
manner;  thick,  unstained  sections  are  to  be  mounted  in  diluted  glycerine 
(Fig.  252). 

No.  192. — The  Alitcous  Membrane  of  the  Olfactory  Region. — Remove 
pieces  3  to  6  mm.  long  of  the  brown  mucosa  from  the  upper  portion  of  the  nasal 
septum  of  a  rabbit  (No.  190),  and  place  them  for  3  hours  in  20  c.c.  of  Ran- 
vier's alcohol,  which  loosens  somewhat  the  elements  of  the  olfactory  epithelium. 
Transfer  the  pieces  carefully  to  3  c.c.  of  2  per  cent,  osmium  solution  plus  3 
c.c.  of  distilled  water,  and  place  the  whole  for  from  15  to  24  hours  in  the  dark. 
At  the  expiration  of  this  time  the  pieces  are  to  be  placed  for  a  half  hour  in  20 
c.c.  of  distilled  water  and  then  hardened  in  30  c.c.  of  gradually  strengthened 
alcohol.  The  hardened  pieces  are  to  be  embedded  in  liver  and  sectioned. 
Stain  the  sections  20  to  30  seconds  in  Bohmer's  hematoxylin  :  mount  them  in 
damar. 

In  order  to  obtain  good  views  of  the  glands  make  thick  sections  transverse 
to  the  course  of  the  Jierve-fibcrs  (Fig.  255).  For  the  exhibition  of  the  nerve- 
libers  and  the  epithelium  thin  sections  parallel  to  the  course  of  the  fibers  are 
suitable  (Fig.  256). 

No.  193.  —  The  neiTe-processes  of  the  olfactory  cells  may  be  obtained  in 
preparations  made  according  to  No.  178.  In  these  the  duct-system  of  the 
olfactory  glands  is  often  blackened. 

No.  194. — For  orientation  "with  regard  to  the  number  and  position  of  the  taste- 
buds  proceed  according  to  the  method  in  No.  96.  Suitable  objects  are  the  cir- 
cumvallate  i)apillae  of  any  animal  and  the  papillae  foliatse  of  the  rabbit.  The 
latter  consist  of  elevated  groups  of  parallel  folds  of  the  mucosa,  found  one  on 
either  edge  of  the  root  of  the  tongue.      In  moderatelv  thin  sections  vertical  to 


SPECIAL    TECHNIQUE.  325 

the  long  axis  of  the  folds,  examined  with   the  low  power,  the   taste-buds   may 
be  recognized  as  clear  spots. 

No.  195. — The  Structure  of  the  Taste-buds. — Dissect  off  with  scissors  a 
papilla  foliata  of  a  rabbit,  with  as  little  as  possible  of  the  subjacent  muscle 
substance.  Pin  the  piece  with  spines  on  a  cork-stopper,  the  muscle  side  toward 
the  cork,  and  expose  it  for  i  hour  to  the  vapor  of  osmic  acid  (see  further  p. 
28,  6).  Thin  sections  of  the  hardened  preparation  embedded  in  liver  are  to 
be  stained  30  seconds  in  Bohmer's  hematoxvlin  and  mounted  in  damar 
(Fig.  258)- 

Xo.  196. — Exhibition  of  the  Xer-ces. — Cut  out  with  scissors  a  circumvallate 
papilla  (without  the  wall),  and  place  it  for  10  minutes  in  the  filtered  juice  of  a 
lemon;  then  transfer  it  to  5  c.c.  of  a  i  per  cent,  gold-chloride  solution  and 
place  the  whole  for  i  hour  in  the  dark.  Lift  the  papilla  with  wooden  rods 
from  the  gold-chloride  solution  into  a  watch-glass  with  distilled  water  and  wash 
it  by  moving  it  to  and  fro.  Transfer  it  to  20  c.c.  of  distilled  water  to 
which  3  drops  of  acetic  acid  have  been  added.  In  this  expose  the  pa[>illa  to 
daylight  until  the  reduction  is  completed,  which  usually  requires  3  days.  Harden 
the  papilla,  in  the  dark,  in  30  c.c.  of  gradually  strengthened  alcohol.  Embed 
the  object  and  make  the  thinnest  possible  sections.  Mount  in  damar.  The 
nerve-fibers  are  dark-red  to  black,  the  gustatory  cells  are  also  dark  (compare 
with  Fig.  259). 

The  papillae  foliatse  of  the  rabbit  are  not  suitable  for  such  preparations,  but 
yield  successful  preparations  byGolgi's  method  (p.  35  ).  Place  the  papillae  for 
3  days  in  the  osmio-bichromate  mixture,  for  2  days  in  the  silver  solution.  The 
double  method  is  to  be  recommended.  The  intergemmal  fibers  are  more 
numerous  and  more  readily  blackened  than  the  intragemmal  fibers,  which  are  ■ 
exceedingly  delicate.  Frequently  single  cortical  and  gustatory  cells  become 
blackened. 


APPENDIX. 

MICROTOME  TECHNIQUE. 


THE  MICROTOME. 

The  most  useful  microtomes  are  constructed  according  to  two  different 
principles. 

The  principle  of  the  one  kind  consists  therein,  that  the  object  to  be  sec- 
tioned is  elevated  by  the  shifting  of  the  object-holder  up  an  inclined  plane. 

In  the  other  form,  the  object  is  elevated  in  a  vertical  direction  by  a 
micrometer-screw. 

pjoth  kinds  are  excellent  instruments.*  All  parts  of  the  microtome  should 
be  kept  as  clean  as  possible.  It  should  be  protected  from  dust,  when  not 
in  use,  by  covering  it  with  a  light  wooden  case.  The  slideway  in  which  the 
knife  moves  must  be  kept  scrupulously  clean.  It  should  be  cleansed  occasionally 
with  a  cloth  moistened  in  benzine  and  should  then  be  freely  lubricated  with  vase- 
line, so  that  the  sliding-block  will  pass  evenly  throughout  the  entire  slideway 
at  the  lightest  touch.  Especial  care  must  be  bestowed  upon  the  knife.  Only 
with  a  very  sharp  knife  can  very  thin  sections  be  made  or  ribbon  cutting  be 
done.  A  really  sharp  knife  should  pass  easily  through  a  thin  hair  held  at  one 
end  between  the  fingers. 

EMBEDDING. 

P.ARAFFiN  Method. 

The  following  materials  and  apparatus  are  required  : — 
I.  Paraffin:  two  kinds,  a  soft  (melting  point  45°  Celsius)  and  a  hard 
(melting  point  52°  Celsius).  Of  this  prepare  a  mixture  which  melts  at  50° 
Celsius.  On  the  proper  proportions  of  the  two  sorts  of  paraffin  in  the  mixture 
much  depends.  Many  a  failure  is  due  to  an  unsatisfactory  mixture.  The 
precise  proportions  cannot  be  given  because  the  consistence  of  the  paraffin 
depends  in  a  great  measure  on  the  outer  temperature.  Then,  too,  hard 
objects,  as  well  as  the  cutting  of  very  thin  sections,  require  a  harder  mixture 
than  usual.  For  winter,  at  a  room-temperature  of  20°  Celsius,  a  mixture 
of  30  grams  of  soft  and  25  grams  of  hard  paraffin  f  answers  for  most  purposes. 

*  The  workmanship  of  tlie  sliding  microtomes  of  Thoma,  made  by  Jung  in  Heidelberg, 
is  exquisite,  as  I  know  from  my  own  experience.  The  size  No.  IV  is  especially  to  be  recom- 
mended. For  several  years  I  have  used  the  microtome  of  .Schanze  in  Leipzig,  Model  B,  No.  9, 
the  construction  of  which  leaves  nothing  further  to  be  desired.  The  microtomes  constructed  on 
the  same  principle,  byG.  Mihe  in  Hildesheim,  are  also  to  be  highly  recommended  ;  and  very 
good  are  those  of  A.  Becker  in  Gottingen.  [A  very  satisfactory  sliding  microtome  is  made  by 
the  Bausch  and  Lomb  Optical  Company  of  Rochester,  N.  Y.] 

f  To  be  obtained  of  Dr.  Griibler,  Leipzig. 

1:26 


MICROTOME    TECHNIQUE.  327 

2.  Chloroform  :    20  c.c. 

3.  Paraffin-chlflrofonn :  a  saturated  solution  (5  grams  of  the  paraffin 
mixture  and  25  c.c.  of  chloroform).  This  solution  is  litiuid-  at  room- 
temperature. 

4.  An  emhcdding  oven  of  block-tin  with  double  walls,  between  which  is  a 
space  to  be  filled  with  water.  *  A  small  gas-burner  is  to  be  placed  beneath  the 
oven.  On  top  there  are  two  openings  ;  the  one  leads  into  the  space  between 
the  walls,  and  into  this  a  Reichert  thermo-regulator  f  is  to  be  inserted  ;  the  sec- 
ond Oldening  leads  into  the  air-space  or  oven,  and  into  this  a  thermometer  is  to 
be  inserted.  The  front  wall  consists  of  a  glass  plate  which  slides  up  and  down 
in  grooves.  The  interior  of  the  oven  is  divided  into  three  compartments 
by  means  of  two  adjustable  shelves.  The  oven  should  be  25  cm.  long,  23 
cm.  high,  and  16  cm.  deep.  The  embedding  oven,  with  its  accessories,  is 
indisjiensable  if  much  embedding  in  paraffin  is  to  be  done;  however,  the 
paraffin  may  be  melted  on  a  water-bath  and  kept  liquid  with  a  small  spirit- 
flame. 

5.  An  Embedding  Frame. — This  consists  of  two  adjustable  bent  metal 
frames,  placed  together  thus 

^^ 

Instead  of  this  frame  little  paper  trays  madeofstiff])aper  or  cardboard  can  be  used. 
The  objects  to  be  embedded  must  be  absolutely  free  from  water,  and  to  this  end 
should  have  lain  3  days  in  absolute  alcohol,  which  has  been  changed  several 
times  ;  they  are  then  to  be  transferred  to  a  bottle  containing  20  c.c.  of  chloro- 
form, in  which  they  should  remain  until  the  following  day.  From  this  the 
objects  should  be  carried  to  the  solution  of  paraffin  in  chloroform  and,  in  from 
2  to  8  hours,  according  to  their  size,  transferred  to  a  capsule  containing 
melted  (but  not  too  hot )  paraffin.  In  about  a  half  hour  the  objects  are  to  be 
transferred  to  a  second  capsule  with  melted  paraffin,  +  where,  according  to 
their  size,  they  are  to  remain  from  i  to  5  hours. §  The  paraffin  should  not  be 
heated  more  than  2  to  3  degrees  above  its  melting  point ;  for  the  mixture  advised 
the  air  in  the  oven  should  have  a  temperature  of  50°  Celsius.  When  the  ob- 
jects have  been  in  the  i)araffin  bath  the  required  length  of  time,  place  a  slide 
in  a  broad  dish  and  on  this  the  embedding  frame,  into  which  the  paraffin  and 
object  are  now  to  be  poured.  Then,  while  the  paraffin  is  still  fluid,  with  a 
heated  needle  place  the  object  in  the  desired  position  ;  so  soon  as  this  is  done 
carefully  pour  cold  water  into  the  dish  until  it  reaches  the  upper  margin  of 
the  frame  ;  the  paraffin  will  begin  at  once  to  harden,  whereupon  more  water 
may  Ite  added  until  the  entire  frame  is  submerged.  By  this  manipulation  the 
paraffin  hardens  into  a  homogeneous  mass,  whereas  otherwise  it  is  apt  to  crys- 
tallize and  is  then  difficult  to  cut  and  also  has  an  injurious  influence  on  the  struc- 
ture of  the  embedded  tissues.  In  about  10  minutes  the  metal  frames  maybe 
removed  ;  the  paraffin  block  should  be  allowed  to  remain  in  the  water  on  the 
slide  until  it  is  completely  hard. 

The  embedded  object  may  be  sectioned  in  a  half  hour.  In  case  it  is  to  be 
used  later  mark  it  with  a  needle.  In  the  paraffin  the  object  can  be  kept  for 
an  indefinite  period. 

*  Made  by  R.  Jung,  Heidelberg. 
t  To  be  obtained  of  Reichert,  Vienna. 

%  If  the  paraffin  has  been  melted  on  a  water-bath,   place  the  flame  at  such  a  distance  that 
the  surface  of  the  paraflfin  remains  covered  by  a  thin  film. 

\  This  is  sufficient  for  all  cases  ;  for  small  objects  from  I  to  2  hours  will  be  enough. 


328  HISTOLOGY. 


Celloidin  Method. 

Two  solutions  are  required  : — 

a.  A  thin  solution  of  about  30  grams  of  celloidin  cut  into  cubes  are  to 
be  dissolved  in  60  c.c.  of  a  mixture  of  equal  parts  of  absolute  alcohol  and 
ether. 

d.  A  somewhat  thicker  solution  of  30  grams  of  celloidin  dissolved  in 
40  c.c.  of  a  mixture  of  equal  parts  of  absolute  alcohol  and  ether.  This  solu- 
tion has  the  consistence  of  a  thick  syrup. 

Both  solutions  should  be  kept  in  wide-necked  bottles.  If  they  become  too 
thick  they  may  be  thinned  by  the  addition  of  some  of  the  alcohol-ether  mix- 
ture. After  a  time  the  solutions  become  turbid  and  milky ;  it  is  better  then  to 
let  them  dry  completely  and  to  redissolve  the  pieces  in  the  alcohol-ether 
mixture. 

The  tissues  to  be  embedded  must  be  completely  free  from  water  and  must 
have  lain  i  to  2  days  in  absolute  alcohol,  which  has  been  changed  several 
times.  From  this  the  objects  should  be  transferred  to  the  thin,  and  on  the  follow- 
ing day  to  the  thick,  celloidin  solution.  In  the  latter,  the  objects  may  remain 
for  an  indefinite  length  of  time.  Usually  they  are  sufficiently  permeated  after  24 
hours,  but  large  objects  enclosing  many  spaces  must  remain  in  the  thick  solution 
about  8  days.  The  object  should  then  be  quickly  placed  on  a  cork-stopper  and 
some  celloidin  poured  over  it.  In  doing  this  care  must  be  taken  not  to  press 
the  object  against  the  cork,  lest  it  become  detached.  There  should  be  a  stra- 
tum of  celloidin  I  to  2  mm.  thick  between  the  cork  and  the  object.*  Now  the 
whole  is  to  be  placed  under  a  bell-glass  to  dry  slowly  ;  the  bell-glass  should  not 
be  air-tight,  and  to  avoid  this  should  be  supported  on  one  side  on  a  needle  or 
something  similar.  Delicate  objects  dry  in  a  half  hour,  larger  objects  in  4 
hours;  they  are  then  to  be  placed  in  a  glass  jar  with  30  c.c.  of  80  per  cent, 
alcohol.  In  order  that  the  objects  may  be  submerged,  glue  the  under  surface 
of  the  cork-stopper  by  means  of  celloidin  to  the  inner  surface  of  the  lid  of  the 
jar.  On  the  following  day  the  alcohol  should  be  replaced  by  70  per  cent. 
alcohol,  in  which  the  tissue  may  remain  an  indefinite  length  of  time. 

In  order  to  cut  thin  sections  the  celloidin  must  be  hardened  :  for  this  pur- 
pose transfer  the  objects  embedded  in  celloidin  from  the  80  per  cent,  alcohol 
for  2  days  or  longer  into  an  alcohol-glycerine  mixture  (80  per  cent,  alcohol 
one  part,  pure  concentrated  glycerine  6  to  10  parts).  The  larger  the  propor- 
tion of  glycerine  to  alcohol,  the  harder  the  celloidin  becomes.  This  mixture 
may  be  differently  prepared  ;  an  extreme  limit  is  i  part  of  alcohol  to  30  parts 
of  glycerine.  Still  greater  difference  in  the  proportions  produces  strong  curl- 
ing of  the  sections.  In  order  to  prevent  the  yielding  of  the  elastic  cel- 
loidin block,  dry  it  carefully  with  filter-paper  on  removing  it  from  the  alcohol- 
glycerine  mixture  ;  make  a  pair  of  lateral  incisions  and  dip  it  into  liquid 
paraffin  ;  such  blocks  cannot  be  preserved  dry — they  must  be  returned  to  the 
alcohol-glycerine  mixture. 

Preparations  fixed  by  Golgi's  method  reijuire  special  treatment,  since  the 
absolute  alcohol  has  an  injurious  influence  if  the  object  remains  in  it  bevond  i 
hour.  When  the  tissue  is  taken  from  the  silver  solution  it  is  to  be  placed  in  30 
c.c.  of  96  per  cent,  alcohol,  15  to  20  minutes,  then  hardened  in  absolute  alcohol 
for  15  minutes,  and  then  .placed  in  the  thin  celloidin  solution  for  5  minutes. 
Meanwhile,  in  the  previously  smoothed  lateral  surface  of  a  broad  piece  of  elder- 

*  This  stratum  must  not  be  thicker ;  even  well-hardened  celloidin  is  elastic,  and  a  thick 
layer  would  cause  the  object  to  give  in  sectioning. 


MICROTOME    TECHNInl'K.  329 

pith,  make  an  excavation  just  large  enough  to  take  in  the  whole  preparation  ;  in- 
sert it,  cover  it  with  celloidin  solution,  and  then  fit  a  second  piece  of  elder-pith 
on  the  first,  pour  on  more  celloidin,  and  place  the  whole  for  5  minutes  under 
a  bell-glass  to  dry  ;  then  transfer  it  to  80  per  cent,  alcohol  for  5  minutes,  and 
cut  sections  with  a  knife  flooded  with  80  per  cent,  alcohol.  The  microtome 
is  altogether  unneces.sary  ;  satisfactory  sections  can  easily  be  cut  free-hand.  If 
the  microtome  be  used,  the  thickness  of  the  sections  should  vary  from  40  to 
120  IX.  The  elder-pith  should  be  trimmed  off  so  that  only  a  small  border 
(i  mm.)  surrounds  the  celloidin. 

SECTIONING. 

Paraffin  Ohjecis  wi/h  llie  Knife  Placed  Obliquely. — The  paraffin  block  con- 
taining the  ti.ssue  is  to  be  secured  in  a  hollow  cylinder  coated  with  hard  ])araffin 
(in  the  Thoma  microtome)  or  (in  the  microtome  of  Schanze)  to  a  little  plate 
adjoining  the  clamp.  With  the  latter  the  plate  is  simply  warmed  and  the 
paraffin  block  glued  to  it  by  pressure.  In  the  case  of  the  cylinder,  warm  it 
and  also  the  base  of  the  paraffin  block ;  press  the  latter  lightly  into  the  cylin- 
der and  by  means  of  a  heated  needle  inserted  between  them  establish  a  firm 
union.  In  order  to  cool  the  paraffin  quickly  place  the  cylinder  or  the  ])late 
for  5  minutes  in  cold  water.  The  projecting  portion  of  the  paraffin  block 
containing  the  object  should  then  be  trimmed  to  a  four-sided  column,  the  ba.se  of 
which  is  a  right-angled  i)arallelogram. 

The  column  must  not  be  taller  than  i  cm.,  and  the  object  should  be  cov- 
ered by  a  layer  of  paraffin  not  over  i  to  2  mm.  thick.  The  cylinder  (or  the 
plate)  with  the  object  should  now  be  placed  in  the  microtome.  Sections  are 
to  be  cut  with  the  blade  of  the  knife  dry.  The  position  of  the  knife  depends 
on  the  nature  of  the  object. 

Sectioning  with  the  Knife  Placed  Ohliqiiely. — If  the  object  is  large  and  of 
unequal  resistance  the  knife  should  be  so  clamped  that  it  forms  a  very  acute 
angle  with  the  long  axis  of  the  microtome.  The  paraffin  block  should  stand 
so  that  the  knife  strikes  it  first  on  one  corner.  The  knife  should  be  moved 
slowly  in  the  slideway  and  pressure  upon  it  should  be  carefully  avoided. 

Sectioning  li'ith  the  Knife  Placed  Transversely. — Screw  the  knife  down 
jierpendicular  to  the  long  axis  of  the  microtome,  turn  the  i)araffin  block  so 
that  the  blade  will  strike  it  first  on  a  flat  surface.  The  knife  should  be  moved 
rapidly  with  a  ])laning  movement  and  then  the  sections  will  adhere  to  one 
another  at  their  edges  and  form  long  ribbons.  When  the  paraffin  is  of  the  right 
consistence  the  first  section  lies  smooth  on  the  blade  and  is  shoved  by  the  second 
section  in  the  direction  of  the  back  of  the  blade.  If  however  the  first  sections 
show  an  inclination  to  curl  and  fall  over  the  edge,  they  must  then  be  carefully 
held  with  a  delicate  sable  brush  and  led  back  to  the  right  direction.  Ribbon 
cutting  is  most  successful  when  the  sections  have  a  thickness  of  o. 01  of  a  mm.  ; 
thicker  sections  curl  easily  and  do  not  readily  adhere  to  one  another  at  their 
edges. 

Ol'stacles  in  Sectioning  and  their  Remedy. — P^very  one  who  has  worked 
with  paraffin  is  probably  able  to  explain  many  an  unsuccessful  attempt. 

I.  The  knife  glides  over  the  object  and  cuts  a  partial  section  or  none. 
The  reason  for  this  may  lie  in  the  microtome  ;  the  slideway  may  not  be  clean  ; 
examine  the  vertical  portion  of  the  slideway.  Or  the  knife  is  not  sharp 
enough,  or  the  under  surface  has  paraffin  attached  to  it  ;  in  the  latter  case 
remove  the  knife  and  with  a  cloth  wetted  with  turpentine  carefully  cleanse  it. 
Knives  with  thin  backs  buckle  when  the  distal  end  of  the  blade  is  used  ;  thus 
it    happens   that  when    the    knife   is  obliquely  placed    the  blade  strikes  the 


330  HISTOLOGY. 

tissue  at  first  and  glides  over  the  rest  without  cutting  it.  In  microtomes  of 
earlier  construction  the  cause  of  this  often  lies  in  the  unsatisfactory  manner  in 
which  the  block  of  paraffin  is  secured. 

Secondly,  the  trouble  may  be  found  in  the  object  ;  it  may  be  too  hard, 
or  of  very  unequal  resistance,  or  poorly  embedded  ;  in' the  latter  case  there  are 
two  possibilities.  Either  the  preparation  was  not  thoroughly  dehydrated,  in 
which  case  it  e.xhibits  opaque  spots,  or  it  still  contains  chloroform  ;  in  this  case 
it  is  soft,  and  light  pressure  with  a  needle  on  the  surface  leaves  a  mark  or  even 
presses  out  fluid.  In  both  cases  the  procedure  of  embedding  must  be  repeated, 
reversing  the  series  of  processes  to  the  absolute  alcohol  (in  the  latter  case  to 
the  paraffin  bath). 

Finally,  the  consistence  of  the  paraffin  may  be  at  fault. 

2.  The  sections  curl.  This  can  be  prevented  by  holding  a  small  sable 
brush  or  bent  needle  lightly  against  the  curling  sections.*  The  cause 
of  this  curling  lies  in  the  hardness  of  the  paraffin,  which  is  also  responsible 
for— 

3.  The  sections  break.  The  serviceableness  of  the  paraffin  depends  in  a 
high  degree  on  the  outer  temperature.  If  the  paraffin  is  too  hard  do  not  endeavor 
to  reduce  its  consistence  by  the  admixture  of  soft  paraffin, — this  is  the  last 
resource, — but  employ  simpler  measures.  Cut  the  sections  near  a  stove  or  near 
a  lamp  ;  often  slight  warming  of  the  knife  is  sufficient.  Even  very  good 
paraffin  crumbles  when  cut  with  a  cold  knife. 

4.  The  sections  fold  and  become  pressed  together.  As  a  result  of  this  the 
sectioned  objects  acquire  a  false  form.  The  reason  for  this  lies  in  a  too  soft 
paraffin.  This  difficulty  may  be  overcome  by  placing  the  block  frequently  in 
cold  water  or  by  cutting  the  sections  in  a  cold  room  (in  summer,  in  the  morn- 
ing hours). 

Cclloidin  Objects. — The  embedded  object  is  to  be  trimmed  so  tliat  it  is  sur- 
rounded by  a  stratum  of  celloidin  only  i  to  2  mm.  thick  ;  clamp  the  knife 
obliquely,  so  that  it  makes  a  very  acute  angle  with  the  long  axis  of  the  micro- 
tome. The  knife  must  be  moistened  with  70  per  cent,  alcohol,  by  means  of  a 
sable  brush  ;  this  must  be  repeated  after  every  second  or  third  section.  The 
sections  should  be  removed  with  a  sable  brush  and  transferred  to  a  dish  contain- 
ing 70  per  cent,  alcohol.  Very  thin  sections  (less  than  0.02  mm.)  cannot  be 
cut  unless  the  celloidin  has  been  hardened. 


PRESERV.VnON  OF  THE  SECTIONS. 

Paraffin  Objects. — If  the  sections  are  not  very  thin  and  are  not  in  ribbons, 
they  may  be  placed  in  a  capsule  with  5  c.c.  of  turpentine,  and  when  the  paraffin 
is  dissolved  transferred  to  a  second  capsule  with  turpentine.  From  this  the  sec- 
tions, if  the  tissue  has  been  stained  in  bulk,  are  brought  on  to  a  slide  and 
mounted  according  to  the  directions  given  on  p.  38.  If  the  sections  are  un- 
stained, transfer  them  from  turpentine  to  5  c.c.  of  absolute  alcohol,  which  is  to 
be  changed  in  5  minutes.  In  another  2  minutes  the  sections  may  be  stained. 
In  the  case  of  serial  sections  and  very  thin  sections,  it  is  necessary  to  fasten 
the  dry  sections  on  the  slide.  The  slide  must  be  absolutely  clean  ;  wash  it 
with  alcohol  and  dry  it  with  a  clean,  not  oily,  cloth,  or  place  it  for  a  half 
hour  in  cold  soap-suds.  On  the  well-dried  slide  arrange  the  sections  (or  por- 
tion of  the  "  ribbon  "),  and  at  the  edge  of  the  same  place  a  drop  of  distilled 

*  .\  "  section-smoother  "  Tor  microtomes  in  which  the  object  is  elevated  vertically  is  made 
by  Kleinert  of  Breslau.      See  further  Born,  "  Zeitschr.  f.  wissensch.  Mikroskopie,"  Bd.  .x,  p.  157. 


MICROTOME    TECHNIQUE.  33 1 

water  by  means  of  a  sable  brush.  Another  section  (or  portion  of  the  ribbon) 
is  now  to  be  ])laced  on  the  slide,  another  drop  of  water  added,  and  so  on 
until  the  slide  is  covered.  It  does  not  matter  if  the  sections  float.  Pass  the 
slide  through  a  spirit-flame  or  place  it  i  to  3  minutes  in  the  oven  ;*  on  being 
slightly  warmed,  the  sections  spread  out  flat  and  smooth.  Then  arrange  them 
with  a  needle,  and  by  slightly  inclining  the  slide  let  the  water  flow  off,  or 
absorb  it  with  a  strip  of  filter-paper  and,  protected  from  dust,  let  the  whole 
dry.  On  the  following  day  ])0ur  tnrjientine  over  the  slide  and,  if  the  sections 
are  already  stained,  mount  them  in  damar.  In  case  the  sections  are  not  stained 
the  turpentine  is  to  be  wiped  off  and  the  slide  ]jlaced  in  absolute  alcohol. y 
After  5  minutes  take  the  slide  from  the  alcohol,  which  is  to  be  quickly 
wiped  off  around  the  sections,  and  either  placed  in  the  stain  or  covered 
with  a  drop  of  the  solution.  Then  slowly  transfer  the  slide  to  a  dish  with 
distilled  water  and  preserve  it  in  dilute  glycerine  (p.  37),  or  with  the  cus- 
tomary preliminary  treatment  with  absolute  alcohol  and  oil  of  bergamot  (p.  38), 
mount  it  in  damar. 

Celloidiii  Ohjects. — Place  the  sections  in  a  dish  containing  20  c.c.  of  90 
per  cent,  alcohol.  If  the  tissue  has  not  been  previously  stained  in  bulk,  staining 
in  bulk  is  to  be  preferred,  the  sections  maybe  subsequently  stained  ;  but  aniline 
colors  cannot  be  used,  as  these  also  stain  the  celloidin  ;  even  hematoxylin 
imparts  a  light  blue  tint  to  the  celloidin.  The  sections  must  not  be  placed  in 
alii^olute  alcohol,  since  this  dissolves  the  celloidin  ;  they  are  to  be  taken  from 
the  90  per  cent,  alcohol  and  jjlaced  in  chemically  jmre  amyl  alcohol  and  then 
transferred  to  xylol  ;  when  the  clearing  is  completed  (p.  38)  mount  them  in 
xylol-balsam. 

Serial  sections  of  celloidin  objects  are  only  used  for  special  purposes,  for 
example,  for  the  central  nervous  system.  See  the  articles  by  Wiegert  in  the 
"  Zeitschrift  fiir  wissenschaftliche  Mikroskopie,"  Bd.  ii.,  p.  490,  Bd.  iii.,p. 
480,  Bd.  iv.,  p.  209.  The  negative  varnish  recommended  in  the  article  is  to 
be  obtained  of  Dr.  Griibler. 


•  The  paraffin  must  not  be  allowed  to  melt ;  the  resulting  mixture  of  melted  paraffin  and 
water  is  not  soluble  in  turpentine. 

t  The  turpentine,  also  the  alcohol,  must  be  quickly  wiped  ofT,  because  the  sections  are  ren- 
dered useless  if  they  are  allowed  to  become  dry.  Care  must  also  be  exercised  in  placing  the 
staining  fluid  on  the  sections,  which  it  should  completely  cover.  Loosening  of  the  sections 
occurs  when  there  is  not  enough  water  between  the  section  and  the  slide — the  water  must  be 
evenly  diffused  between  the  two.  The  sections  may  also  be  fastened  to  the  cover-glass,  but  ihis 
method  necessitates  the  use  of  larger  quantities  of  the  staining  solution,  alcohol,  and  other 
reagents. 


INDEX. 


A. 

Acervulus  cerebri,  295 
Acetic  acid.  30 
Acbromatin,  48 
Acid  alcohol,  23 

mixture,  22 
Adenoid  tissue,  68 

diffuse,  96 

of  the  intestines,  166,  167 

of  the  lymph-nodes,  95 

of  the  pharynx,  157 

of  the  tongue,  155 
Adipose  tissue,  66 
Alcohol,  absolute,  19,  27 

acid,  23 

gradually  strenj^thened,  29 

ninety  per  cent.,   19 

Ranvier's  thirty-three  per  cent. 

seventy  per  cent.,  19 
Alum-carmine,  23 
Alveolar  ducts,  185 
Ammonium  picrate,  23 
Amoeboid  movement,  51 
Amphypyrenin,  48 
Anaphase,  53 
Anisotropic  substance,  73 
Arachnoid,  133 

villi  of,  133 
Arcuate  fibers,  237 
Arcus  tarseus,  258 

tarseus  externus,  258 
Areolar  tissue,  64,  67 
Arrectores  pilorum,  227 
Arteries,  85 

classification  of,  85 
Attraction-sphere,  52 
Auerbach's  plexus,  I70,  305 
Axis-cylinder,  77,  81,281,  282 


Haillarger's  stripes,  126 
Basement  membrane,  61,  67 
liergamot  oil,  21 
Uerliii  blue,  37 
liile,  iSi 

Hile-capillaries,  176 
Bioplasts,  48 


Bismarck  brown,  23 
Blood,  91 

elementary  granules,  91 

examination  of,  for  legal  purposes,  286 

fibrin,  92 

hematoblasts,  93 

permanent  preparation  of,  284 

plasma,  91 
lilood-cells,  91 

colored,  91 

colorless,  91 
Blood-crystals,  93,  286,  287 
Blood-platelets,  92,  2S6 
Blood-vessels,  85,  283 

arteries,  85 

blood-vessels  of,  90 

capillaries,  89 

epithelium  (endothelium)  of,  283 

external  clastic  membrane,  88 

internal  elastic  membrane,  S5 

large,  282 

lymph-spaces  of,  90 

nerves  of,  90 

small,   283 

tunica  adventilia,  85 

tunica  intima,  85 

tunica  media,  85 

valves,  89 

vasa  vasorum,  90 

veins,  88 
Bone,  70,  100 

articulations  of,  105 

blood-vessels  of,  104 

canaliculi,  70 

cells,  71,  no 

circumferential  lamella;,  71,  102 

compact  matrix,  70 

development  of,  107,  291 

dried,  289 

endochondral,  I08 

fundamental  lamellx.  102 

ground  lamella',  102 

growth  of,  n  2 

Haversian  canals,  loi,  2S9 

Haversian  lamella",  102,  2S9 

Haversian  systems,  102 

Howship's  lacunce,  X13 

inlerinembranous,  71,  III 

interstitial  lamellx,  71,  102 

lacuna;,  70 

lymph-vessels  of,  105 


333 


Bone,  marrow  of,  I02 

nerves  of,  105 

osteoblasts,  no 

osteoclasts,  113 

perichondral.  III 

periosteal,  71,  108 

periosteum,  104 

primary,  108 

resorption  of,  112 

secondary,  in 

Sharpey  libers,  71,  I04,  289 

spongy  matrix,  70 

Volkmann's  canals,  102 
Bowman's  membrane,  237 
Brain,  123,  295 

cells  of,  295 

cerebellum,  123 

cerebrum,  1 23 

corpora  quadrigemina,  123 

corpora  striata,  1 23 

ganglia  of,  1 27 

Golgi  staining  of,  295 

gray  substance  of,  12  J 

hypophysis  cerebri,  131 

optic  thalami,  123 

pineal  body,  1 32 

staining  of  niedullated  nerve-fibers  of,  295 

ventricles  of,  127 

white  substance  of,  1 23 
Brain-sand,  132,  295 
Bronchi,  185,  30S 

blood-vessels  of,  188 

cartilages  of,  186 

excretory  division,  185 

glands  of,  187 

mucosa  of,  1S7 

muscle-fibers  of,  186 

respiratory  division,  iSS 
Brunner's  glands,  166 
Bursa;,  113,  115 


Cajal's  cell,  125 
Calcification,  center  of,  109 
Canada  balsam, '22 
Canalized  fibrin,  220 
Capillary  blood-vessels,  89 

development  of,  89,  2S4 
Cardiac  muscle,  76 
Carmine,  alum-,  23 

borax-,  23 

neutral  solution  of,  23 
Carotid  gland,  90 
Cartilage,  68,  279 

articular,  106,  291 

bronchial,  186 

capsule,  68 

cells,  68 

costal,  hyaline,  279 

elastic,  68,  279 

epiphyseal,  112 

fibrous,  68,  279 

hyaline,  68,  279 

lacunas  of,  68 

matrix  of,  68 


Cartilage,  perichondrium,  107 

varieties  of,  68 
Cell-division,   51 

direct,  5 1 

duration  of,  53 

indirect,  51 
Cell-membrane,  50 
Cells,  47 

basket,  61 

bone,  71 

Cajal's,  125 

cartilage,  68 

chief,  160 

column,  ilS 

commissure,  I18 

concentric,  245 

cone-visual,  246 

decidual,  216 

Deiters's  122,  126,  265 

endothelial,  56 

ependymal,  122,  126 

epithelial,  55 

fat,  66,  278 

fat,  serous,  67 

fiber,  260 

fixed,  67 

forms  of,  50 

ganglion,  77 

giant,  103 

glandular,  57 

glia,  122 

goblet,  58,  163,  164,  187 

granule,  66,  277 

growth  of,  54 

gustatory,  274 

hair,  260 

interior,  120 

interstitial,   199 

Langerhans's  138,  297 

length  of  life  of,  54 

liver,  175,  307 

marrow,  103 

mossy,  123 

motion  of,  51 

multiplication  of,  51 

nerve,  77,  118 

olfactory,  270 

parietal,  160 

pigment,  66,  225,  239 

pillar,  263 

plasma,  66,  235 

pluricordonal,  120 

prickle,  56,  224 

Purkinje's,  129 

reproduction  of,  51 

rod-visual,  246 

secretory  activity  of,  54 

secretory  products  of.  54 

sexual,  207 

size  of,  50 

spider,  122 

structure  of,  48 

sustentacular,  200,  245,  270,  273 

tegmental,  274 

tendon,  293 

undiflferentiated,  47 

vasoformative,  2S4 


335 


Cells,  vita!  properties  of,  51 

wandering  of,  67 
Cement-substance,  54 
Central  spindle,  53 
Centrosome,  49 
Cerebellum,  1 27,  295 

basket-cells  of,  130 

cells  of  I'urkinje,  129 

Golgi  staining  of,  295 

granule  layer  of,  12S 

molecular  layer  of,  130 

neuroglia  of,  130 

while  substance  of,  131 
Cerebrum,  125,  295 

bundle  of  Vic(|  d'  Azyr,  126 

cells  of  Cajal,  125 

hippocampal  convolution,  1 26 

inlerradial  reticulum,  126 

layer  of  polymorphous  cells,  125 

molecular  layer,  125 

radiating  bundles  of,  126 

stripes  of  liaillarger,  126 

stripes  of  Gennari,  126 

superradial  reticulum,  126 

tangential  libers,  125 

zone  of  large  pyramidal  cells,  125 

zone  of  small  pyramidal  cells,  125 
Cerumen,  269 
Ceruminous  glands,  323 
Chondrin,  69 
Choriocapillaris,  239 
Choroid,  239,  317, 

boundary  zone  of,  239 

choriocapillaris,  239 

layer  of  capillary  networks,  239 

layer  of  large  blood-vessels,  239 

stroma  of,  239 

tapetum  cellulosum,  239 

tapetum  fibrosum,  239 

teased  preparation  of,  317 

vitreous  lamina,  240 
Chromatin,  48 
Chromic  acid,  20 
Chromoacetic  acid,  21 
Chromoaceto-osmic acid,  21,  2S 
Chromosomes,  $2 
Ciliary  body,  236,  240 

muscle,  257 
Ciliated  epithelial  cells,  277 
Cle.iring,  39 
Close  skein,  52 
Coccygeal  gland,  90 
Cochlea,  261.  322,  323 
Cohnheim's  fields,  74 
Coil-glands,  232,   314 

distribution  of,  233 

secretion  of,   233 
Collateral  fibrils,  77 
Colored  blood-corpuscles,  91 

development  of,  93 

hemoglobin,  91 

of  frog,  286, 

of  man,  284 

stroma  of,  91 
Colorless  blood-corpuscles,  2S6 

basophilc  granules  of,  285 

nculrophile  granules  of.  2S5 


Colorless  blood-cor|)Uscles,  oxyphile  granules 

of,  28s 
Colostrum,  236 

corpuscles  of,  236 

elements  of,  316 
Column-cells,  118 
Conarium,  132 
Cone-fibers,  246 

-granules,  246 
Congo  red,  23 
Coni  vasculosa,  202 
Conjunctiva,  palpebral,  256 

scleral,  25S 
Connective  tissue,  64,  277 

arrangement  of  elements  of,  76 

blood-vessels  of,  71 

cells  of,  66,  67,  277 

cell-spaces  of,  72 

elastic,  66 

fibrillar,  64,  277 

intercellular  substance  of,  64,  65 

interstitial,  199 

lymph-spaces  of,  72 

mucous,  64,  277 

nerves  of,  71 

reticular,  97 

varieties  of,  64 

wandering  cells  of,  67 
Conus  meduUaris,  1 17 
Corium,  223 
Cornea,  239,  31S 

anterior  basal  membrane,  237 

anterior  epithelium,  237 

arcuate  fibers  of,  237 

bloodvessels  of,  319 

canaliculi  of.  31S 

corpuscles  of,  237,  319 

methylene-blue  staining  of,  320 

nerves  of,  319 

posterior  basal  membrane.  238 

posterior  endothelium,  23S 

spaces  of,  237 

substance  proper,  237,  318 
Corona  radiata,  209 
Corpora  amylacea,  132,  296 

quadrigemina,  123 

striata,  123 
Corpus  Highmori,  199 
Coipuscles,  articular,  141 

concentric,  190 

corneal,  237 

Grandry's,  139 

genital,  14I 

Hassall's,  190 

Herbst  and  Key-Retzius's.  141 

Malpighian,  98,  191 

Merkel's,  139 

Pacini.in,  140 

salivary,  155,  157 

tactile,  297 

Wagner  and  Meissner's.  14I 
Corpus  luteum.  209 
Corti's  organ,  263 
Cover-glass  cement,  22 
Cover-glasses,   iS 
Crescents  of  Giannuzzi,  62 
Crypts  of  Lieberkiihn,    162 


33^ 


Cumulus  ovigerus,  209 
Cytoblastema.  51 
Cytogenous  tissue,  67 


Dahlia,  alum-carmine,  23 
Damar-varnish,  21,  3S 
Daughter-stars,  53 
Decalcifying,  29 
Decidua  graviditatis,  215 

menstrualis,  214 

placentalis  subchorialis,  221 

reflexa,  215 

serotina,  215 

vera,  215 
Demilunes,  62,  156,  171 
Dendrites,  77 

Dentinal  ligament,  circular,  148 
Dentine,  146 

Descemet's  membrane,  238 
Deutoplasm,  208 
Diarthroses,  105 
Diaster,  53 

Direct  cell-division,  51 
Discus  proligerus,  209 
Drawing,  45 
Duct  of  Hartholin,  171 

of  Bellini,  I9I 

of  Stenson,  171 

of  Wharton,  171 

of  Wirsung  and  Santorini,  172 
Duct-system,  59 
Duodenal  glands,  169 
Dura,  133 


E. 

Ear,  260 

arcus  spiralis,  264 
arteries  of,  267 
auditory  hairs,  261 
auditory  teeth,  263 
blood-vessels  of,  267 
bony  labyrinth,  260 
cells  of  Claudius,  266 
cells  of  Deiters,  265 
cells  of  Hensen,  266 
ceruniinous  glands,  26S 
cochlea,  261 
cristas  acusticie,  260 
cupola,  261 
ductus  cochlearis,  261 
ductus  endolymphaticus,  260 
ductus  perilymphaticus,  267 
endolymph,  260 
epithelium  of  cochlea,  263 
external,  260 
fiber-cells,  260 
foramina  nervina,  263 
glands  of,  267,  26S 
hair-cells,  260 
internal,  260 

labium  tympanicum,  261 
labium  veslibulare,  261 


Ear,  lamina  spiralis  membranacea.  262 

ligamentum  spirale,  262 

limbus,  262 

lymph-channels  of,  267 

maculie  cribrosse,  260 

membrana  basilaris,  263 

membranous  labyrinth,  260 

middle,  260 

mucosa  of  Eustachian  tube.  267 

mucosa  of  tympanic  cavity,  267 

nerves  of,  266,  326 

Nuel's  space,  266 

organ  of  Corti,  263 

otoliths,  261 

perilymph,  260 

pillar-cells,  263 

prominentia  spiralis,  262 

Reissner's  membrane,  262 

saccule,  260 

scala  tympani.  261 

scala  vestibuli,  261 

semicircular  canals,  260 

spiral  organ,  263 

stride  vascularis,  262 

sulcus  spiralis,  261 

tunnel.  264 

tympanic  lamella,  263 

utricle,  260 

veins  of,  267 

vestibular  membrane,  262 

zona  pectinati,  263 

zona  perforata,  263 

zona  tecta,  263 
Egg-protoplasm,  208 
Elastic  fibers,  278 

section  of  thick,  27S 

tissue,  66 
Eleidin,  granules  of,  224 
Elementarj'  granules,  91 

organism,  48 
Embedding,  326 

in  celloidin,  328 

in  paraffin,  327 
Enamel  prisms,  300 
Encircling  fibers,  66,  27S 
End-bulbs,  139,  140,  298 
Endogenous  cell-formation,  53,  69 
Endothelium,  56 
Eosin,  23 

Ependyma  of  the  ventricles.  127 
Epidermis,  223 

strata  of,  224 
Epididymis,  203,  313 
Epiglottis,  185 
Epiphysis,  132 
Epithelium,  55 

ciliated,  55 

columnar,  55 

cuticular  zone  of.  55 

cylindrical.  55 

distribution  of,  56 

germinal,  of  ovary.  207 

glandular,  59 

isolation  of,  26 

of  lens,  251 

of  mucous  membranes.  144 

of  sense  organs,  56 


337 


Kpillielium,  pigmented,  55,  225,  226,  24 

prickle-cells  of,  56,  224 

respiratory,  188,  309 

rod,  55,  171,  193 

secretor)-  activity  of,  57,  58 

transitional,  196 

varieties  of,  56,  57 
Kponychium,  227 
l*-poophoron,  2IO 
Krythroblasts,  93,  103 
Ksophagus,  157,  302 
Kustachian  tube,  267,  323 
Exoplasm,  48 
Kye,  236,  316 

blood-vessels  of,  252,  321 

canal  of  Petit,  252,  255 

canal  of  Schlemm,  255 

choriocapillaris,  239 

choroid,  239 

ciliary  body,  240 

ciliary  muscle,  241 

ciliary  processes,  240 

color  of  iris,  241 

conjunctiva,  256 

cornea,  236 

fovea  centralis,  248 

ganglion  retina,  245 

glassy  membrane,  240 

hyaloid  canal,  255 

hyaloid  membrane,  252 

iridocorneal  angle,  255 

iris,  241 

lacrymal  canaliculi,  259 

lacrymal  caruncle,  25S 

lacrymal  glands,  259 

lacrymal  sac,   259 

lamina  cribrosa,  250 

lamina  fusca  sclera-,  239 

lamina  suprachoroidea,  239 

lens,  251 

ligamentum  pectinatum  iridis,  242 

macula,  248 

naso-lacrymal  duct,  259 

optic  nerve,  249 

era  serrata,  243,  248 

perichoroidal  space,  255 

pigment  layer  of  iris,  241 

plica  semilunaris,  258 

retina,  242 

sclera,  238 

sheaths  of  optic  nerve,  249 

spaces  of  Kontana,  242 

suspensory  ligament  of  lens,  252 

tapetum  cellulosum,  239 

tapetum  fibrosum,  239 

Tenon's  space,  255 

tunica  externa,  236 

tunica  interna,  242 

tunica  media,  239 

venae  vorticosa;,  253 

vitreous  body,  252 

vitreous  lamina,   252 

zone  of  Zinn,  252 

zonula  ciliaris,  252 
Eyeball,  coats  of,  236 

contents  of,  236 

lymph-channels  of,  255 


Eyeball,  nerves  of,  255 

Eyelids,  256,  321 

blood  vessels  of,  258 
caruncula  lacrymalis,  258 
cilia,  256 

fornix  conjunctiva-,  25S 
glands  of,  257,  25S 
integument  of,  256 
lymph-vessels  of,  259 
muscle-fibers  of,  257 
nerves  of,  259 
palpebral  conjunctiva,  256 
plica  semilunaris,  258 
tarsus,  258 


Fallopian  tube,  210 
'    Fasciae,  1 13,  114 

Fenestrated  membranes,  65,  278 
I    Fiber-body,  246 
I    Fiber- crates,  243 
'    Fibers,  arcuate,  237 
I  cone-,  246 

j  encircling,  66 

intergemmal,  275 
intragemmal,  275 
lattice-,  181 
lens-,  251 
moss-,  133 
Fixation  of  tissues,  27 
Flemming's  solution,  21,  28 
Formic  acid,  21 

Fresh  objects,  examination  of,  41 
Frommann's  lines,  83 
Fundus  foveas,  248 


Galactophorous  ducts,  235 
Gall-bladder,  174 
Ganglia,  136 

cerebral,  127 

spinal,  136,  297 

sympathetic,  137,  297 
Ganglion-cells,  fresh,  280 

apolar,  78 

bipolar,  78 

multipolar,  78 

unipolar,  78 
Ganglion  nervi  optici,  249 

retime,  245 

spirale,  266 
Gastric  glands,  160 
Gemmation,  54 
Generatio  x-quivoca,  51 
Genitalia,  222 

glands  of,  222 
Gennari's  stripes,  126 
Germinal  center,  95,  167 
Germ-layers,  47 
Glacial  acetic  acid,  20 
Glands,  59 

accessory  mammary,  235 

accessory  tear-,  258 

alveolar,  60 


338 


Glands,  alveolar  system  of,  60 

Bartholin's,  222 

basement  membrane  of,  6 1 

blood-vessels  of,  62 

Bowman's,  271 

Brunner's,  166 

ceruminous,  268 

classification  of,  59 

coil,  232 

compound  saccular,  60 

compound  tubular,  59 

Cowper's,  205 

dehiscent,  61 

duct-system  of,  59 

duodenal,  166 

excretory  duct  of,  61 

follicle  of,  61 

forms  of,  59 

fundus,  l5l 

Harder' s,  321 

lacrymal,  259 

Littre's,  198 

lobules  of,  61 

lumen  of,  308 

membrana  propria  of,  61 

mammary,  234 

Meibomian,  258 

mixed,  171 

Moll's,  257 

Montgomery,  235 

mucous,  171 

Nuhn's,  156 

olfactory,  271 

periurethral,  198 

pyloric,  161 

salivary,  171 

sebaceous,  227,  231 

serous,  171 

simple  saccular,  60 

simple  tubular,  59 

structure  of,  61 

sudoriparous,  232 

sweat-,  232 

tear,  258 

trachoma,  258 

Tyson's,  232 
Glycerine,  21,  38 
Gold  chloride,  21 
Golgi's  "  black  reaction,"  36 

method,  20 

mixture,  35 
Graafian  follicle,  209 

cumulus  ovigerus,  209 

discus  proligerus,  209 

liquor  folliculi.  209 

membrana  granulosa,  209 

theca  folliculi,  209 
Granula,  48 
Ground-substance,  54 

H. 

Hair,  227,  314,  315 
-bulb,  227 
color  of,  228 
cortical  substance  of,  227 
cuticle  of,  227 


Hair,  development  of,  230,  315 

distribution  of,  227 

elements  of,  314 

follicle  of,  227 

growth  of,  230 

medulla  of,  227 

-papilla,  227 

renewal  of,  231,  3 15 

roots  of,  227 

shaft  of,  227 

shedding  of,  230,  315 
Hair-follicle,  227 

elements  of,  315 
Hardening  of  tissues,  29 
Heart,  85,  282 

annuli  fibrosi,  85 

blood-vessels  of,  86 

endocardium,  85 

lymphatics  of,  86 

muscle-fibers  of,  85 

nerves  of,  86 

valves  of,  86 
Hemalum,  22,  32 
Hematoblasts,  93,  103 
Hematoxylin,  Bohmer's,  22,  31 

Delafield's,  22,  34 

Weigert's,  22 
Hemoglobin,  91 
Henn.ann's  solution,  21,  29 
Howship's  lacuna:,  1 13 
Hyaloid  canal,  255 

membrane,  67,  252 
Hyaloplasm,  48 
Hydatid  of  Morgagni,  204 

sessile,  204 

stalked,  204 
Hydrochinous  developer,  20 
Hydrochloric  .acid,  20,  27 
Hypophysis  cerebri,  131,  295 


I. 

Illumination,  central,  43 
lateral,  43 
oblique,  43 

Indirect  cell-division,  51 

Injecting,  37 

Instruments,  17 

Intercellular  bridges,  56,  225,  72 
substance,  47,  54 

Intermediate  lacun.'e,  100 

Internodal  segments,  83 

Internode,  83 

Interstitial  cells,'l99 
granules,  74 
tissue,  67 

Intestine,  162,  304,  305 
basal  border  of,  163 
blood-vessels  of,  16S,  305 
Brunner's  glands,  l56,  303 
crypts  of  large,  305 
epithelium  of  small,  303 
goblet-cells  of,  163,  164 
Lieberkiihn's  follicles,  162 
lymph-nodules  of,  166 
lymph-vessels  of,  169 


339 


Intestine,  mucosa  of,  163 

muscular  tissue  of,  165,  16S 
nerves  of,  170 
I'eyer's  patches,  166 
regeneration  of  epithelium,  163 
sohtary  follicles  of,  166 
triple  staining  of,  304 
vaivula  conniventes,  163 
villi,  162,  303 

Intraepithelial  nerve-fibers,  297 

Involuntary  muscle,  72 

Iridocorneal  angle,  242 

Iris,  236 

Isolating,  25 

Isotropic  substance,  73 


K. 

Karyokinesis,  51,  276 
Keratohyaline  tyrannies,  224 
Kidney,  19I,  310 

bloodvessels  of,  194,  311 

Bowman's  capsule,  191,311 

connective  tissue  of,  194 

cortex  of,  igi,  310 

duct  of  Hcllini,  191 

epithelium  of,  193 

llenle's  loop,  310 

lymph-vessels  of,  196 

Malpighian  corpuscles  of,  191 

medulla  of,  191 

medullary  rays,  310 

nerves  of,  196,  311 

papilliv  of,  191 

uriniferous  tubules,  191,  310 
Kleinenberg's  solution,  20,  28 


L. 

I.acrymal  glands,  259,  321 
Lamina  cribrosa,  250 

fusca  sclera.',  239 

suprachoroidea,  239 
Lanugo,  228,  232 
Larynx,  184,  30S 

blood-vessels  of,  185 

cartilages,  1S4,  1S5 

lymph-vessels  of,  185 

nerves  of,  185 

solitary  n(xlules  of,  184 

vocal  cords,  184 
Lens,  236 

epithelium  of,  320,  321 
Lens-capsule,  252,  320,  321 
Lens-fd)ers,  251,  320 
Leucocytes,  91,  95 

classification  of,  92 

formation  of,  95 

granules  of,  95 
l.igamentum  iridis  pectinatum,  242 
Linin,  48 

Lithium  carbonate,  solution  of,  22 
Littre's  glands,  19S 
Liver,  174,  307 

bile-capillaries,  176 

blood-vessels  of,  177,  308 


Liver,  capsule  of,  180 

capsule  of  (Ilisson,  171,  181 

cells  of,  175,  307 

cords  of  cells,   176 

hepatic  duct,  174 

interlobular  bile-ducts,  174 

interlobular  connective  tissue,  174 

lobules  of,  174,  183,  307 

lymphatics  of,  181 

nerves  of,  I  Si 

relation  of  bile-capillaries  to  cells  of,  177 

secretion  of,  181 

tubular  structure  of,   181,  183 

vasa  aberrantia,   174 
Loose  skein,  52 
Lumen  of  glands   by  Golgi's  black  reaction, 

308 
Lungs,  185,  309 

alveolar  ducts,  185 

alveoli,  155 

blood-vessels  of,  188,  309 

elastic  fibers  of,  188,  309 

infundibula  of,  186 

interlobular  tissue  of,  188 

lobules  of,  1 86 

lymph-vessels  of,  1S9 

nerves  of,  1 89 

pigmentation  of,  1 88 

respiratory  bronchioles,   1S5 

respiratory  epithelium,  188 

terminal  bronchioles,  185 

terminal  vesicles,  186 
Lunula  of  nail,  227 
Lymph,  97 

canaliculi,  72 

corpuscles,  72 

spaces,  72 
Lymph-spaces,  adventitial,  90 

perivascular,  90 
Lymphatic  tissue,  95 

diffuse,  96,  166 
Lymph-channels  of   the  central   nervous  sys- 
tem, 134 
Lymph-nodes,  94,  lOfi,  287 

blood-vessels  of,  96 

bronchial,  189 

distribution  of,  97 

germinal  center,  95 

hilus  of,  94 

medullary  cords,  94 

nerves  of,  96 

peripheral,  96 

pulp  of,  96 

secondary  nodules,  94 

-sinus,  95 

solitai-y,  96,  1 66,  184 

trabecuhv  of,  95 
Lymph- vessels,  93,  287 

origin  of,  94 

stomata,  94 


Macula  lutea,  24S 
Mammary  glands,  234,  316 
accessory,  235 


34° 


Mammary  glands,  ampulla  of,  234 

ducts  of,  235 

nipple,  235 

secretion  of.  236 

sinus  lactiferus,  234 
Margarin  crystals,  67 
Marrow,  cells  of,  103 

elements  of,  103 

red,  102,  290 

yellow,  102 
Mastzellen,  66,  277 
Measurement,  45 
Medullary  rays,  191 

segments,  82 
Meissner's  plexus,  170,  305 
Membrana  chorii,  219 

choriocapillaris,  239 

granulosa,  209 

limitans  iridis,  241 

limitans  olfactoria,  271 

propria,  144 

reticularis,  265 

tectoria,   266 

vestibularis,  262 
Metakinesis,  53 
Metaphase,  53 
Methyl -violet  B,  23,  ;i;i 
Methylene  blue,  23 

for  axis-cylinders,  34 
Microscope,  care  of,  17 

management  of,  43 
Microsomes,  48 
Microtome,  326  ' 

Mikron,  50 

Milk,  human,  236,  316 
Mitotic  cell-division,  51 

in  the  intestine,  163 

in  the  lymph-nodes,  95 
Molecular  motion,  51 
Monaster,  53 
Mother-star,  53 
Motor  nerve-endings,  299 
Mounting,  38 

Mucous  glands  of  lips,  300 
Mucous  membranes,  structure  of,  144 

of  the  oral  cavity,  144,  145 
Muller's  fluid,  20,  28 
Muscle,  72,  113,  293 

bundles  of  striped,  292 

cardiac,  76 

endomysiuni,  113 

epimysium,  II3 

nonstriated,  72 

perimysium,  113 

striated,  73 
Muscle-columns,  74 
Muscle-fibers,  72,  279 

branched,  280 

ends  of,  280 

librillje  of,  74,  280 

isolation  of,  26 

nuclei  of,  74,  280 

pale,  75 

red,  75 

sarcolemma,  75 

smooth,  72,  280 

striated,  73,  279 


Myelin,  82 
Myeloplaxes,  103 


N. 


Nails,  226,  314 

elements  of,  314 

growth  of,  226 

lunula,  227 

matrix  of,  226 

substance  of,  227 
Nasal  mucous  membrane,  269 

basal  cells,  271 

blood-vessels  of,  273 

lymph-vessels  of,  273 

membrana  limitans  olfactoria,  271 

nerves  of,  272,  324 

olfactory  cells,  270,  324 

olfactory  glands,  271 

olfactory  region  of,  270,  324 

respiratory  region  of,  269,  324 

sustentacular  cells  of,  270 

tunica  propria  of,  27 1 

vestibular  region  of,  269 
Nerve-cells,  77 

of  the  first  type,  79 

of  the  second  type,  79 

processes  of,  78 
Nerve-endings,  138,  297 

end-bulbs,  139 

in  epithelium,  138 

in  striated  muscle,  142 

motor,  142,  299 

tactile-cells,  139,  297,  298 

tactile  corpuscles,  I40 

sensory,  138 
Nerve-fibers,  78,  281 

axis-cylinder,  81 

bundles  of,  296 

medullary  sheath  of.  Si,  2S1 

medullated,  Si,  2S1 

neurilemma,  S3 

nodes  of,  83 

nonmeduUated,  80,  282 
Nerve-process,  76 
Nerve-trunks,  134 

blood-vessels  of,  136 

cerebro-spinal,  134 

endoneurium,  135 

epineurium,  134 

fibrillar  septa  of,  135 

lymphatics  of,  136 

perineurium,  134 

sympathetic,  135 
Neuroblasts,  76 
Neurodendron,  77 
Neuro-epithelium,  56 

of  ear,  260 

of  nose,  270 

of  retina,  246 

of  tongue,  273 
Neuroglia,  83,  117,  122,  126 
Neuron,  77 
Neuroplasm,  82,  S3 
Nitric  acid,  20,  28 
Node  of  Ranvier,  83,  282 
Normal  salt  solution,  19 


341 


Xuclear  spindle,  53 

structure,  276 
Nuclei  of  motor-plates,  299 
Nuclein,  48 
Nucleolus,  49 
Nucleus,  48 

matrix  of,  48 

membrane  of,  49 

network  of,  49 

nucleolus,  49 
Nulin's  glands,  156 


O. 

Odontoblasts,  71,  I48,  150,300 

Ocular-micrometer,  45 

Olfactory  cells, 

nerve-process  of,  324 

(Jmentum,  308 

Ora  serrata,  243,  248 

Organ  of  Giraldds,  204 

Osmic  acid,  21,  28 

Osmio-bichromate  mixture,  20 

Ossification,  loS 
centers  of,  109 
endochondral,  109 
metaplastic  mode  of,  1 1 1 
neoplastic  mode  of,  1 1 1 
perichondral ,  I  n 
periosteal,  ill 

Osteoblasts,  no 

Osteoclasts,  113 

Otoliths,  261,  322 

Ova  of  frog,  313 

Ovary,  206,  311,  313 

blood-vessels  of,  2io 
corpus  luteum,  209 
cortex  of,  206 
germinal  epithelium,  207 
glandular  substance  of,  206 
Graafian  follicles,  206 
lymph-vessels  of,  210 
medulla  of,  206 
nerves  of,  210 
primary  egg- tubes,  207 
primary  follicles,  207 
sexual  cells  of,  207 
tunica  albuginea  of,  206 

f)viduct.  210,  313 

Ovula  Nabothi,  214 

Ovum,  207,  313 

corona  radiata,  209 
deuloplasm,  208 
germinal  spot,  209 
germinal  vesicle,  209 
perivitelline  space,  209 
vitellus,  20S 
zona  pellucida,  207 


P. 

Pacchionian  bodies,  133 
Pacinian  bodies,  140 
Pal's  mixture,  22 
Pancreas,  172.  307 

z)Tnogcn  granules  of,  172 


Panniculus  adiposus.  223 
Papillx,  circumvallate,  154 

filiform,  153 

foliate,  154,  274 

fungiform,   154 
Paradidymis,  204 
Paranuclcin,  48 
Paroophoron,  210 
Parotid,  171,  306 
Parovarium,  210 
Pars  retinae  ciliaris,  249 

iridica,  241 

optica,  243 
Pelvis  of  kidney,  311 

epithelial  cells  of,  311 
Penis,  205 

arteries  of,  205 

corpora  cavernosa,  205 

corpus  spongiosum,  206 

erectile  tissue  of,  205 

helicine  arteries,  205 

tunica  albuginea  of,  205 

venous  spaces  of,  205 
Perichondrium,  106 
Perichoroidal  space,  255 
Periosteum,  loi,  104 
Peritoneum,  183 

endothelium  of,  308 
Perivascular  lymph-spaces,  90 
Permanent  preparations,  storing  of,  42 
Peyer's  patches,  96,  166,  167,304 
Pharyngeal  tonsil,  157 
Pharynx,  157 

Picric  acid,  20 
Picrocaniiine,  23,  ^^ 
Picrosulphuric  acid,  20,  28 
Pigmentation  of  skin,  225 

theories  of,  225,  226 
Pineal  body,  132 
Pituitary  body,  131 
Placenta,  217 

amnion,  219 

arteries  of,  212 

blood-vessel  system  of,  212 

canalized  fibrin,  220 

cell-patches,  220 

chorion,  217 

chorionic  villi,  217,  219 

decidua  serotina,  217 

foetal  is.  217 

intervillous  spaces,  217.  Jin 

septa  of,  221 

syncytium,  220 

uterina,  217,  221 
Plasma-cells,  66 
Plastin,  48 

Platino-aceto-osmic  mixture,  21.  2q 
Platinum  chloride,  21 
Pleura,  188 
Plexus  choroideiv,  133 
Polar  field,  52 

radiation,  53 
Potash  lye,  21,  26 
Potassium  bichromate,  20 

permanganate,  22 
Prophase,  52 


342 


Prostate  body,  204,  313 

glandular  tissue  of,  205 
muscular  tissue  of,  204 
secretion  of,  204 

Prostatic  crystals,  204 

Protoplasm,  48 

Pyramids  of  Kerrein,  191 

Pyrenin,  48 


Radial  fibers  of  Muller,  243 
Reagents,  19 

Reissner's  membrane,  262 
Remak's  fibers,  80 
Respiratory  epithelium,  309 
Rete  testis,  199 
Retia  mirabilia,  94 
Retina,  243,  317 

cerebral  layer,  243 

cone-visual  cells,  246 

elements  of,  317 

fovea,  248 

macula,  248 

neuro-epithelial  layer,  246 

era  serrata,  24S 

pigmented  epithelium  of,  248 

rod-visual  cells,  246 
Rod-fibers,  246 
Rod-granules,  246 


Saccule,  260 
Saflfranin,  23,  33 
Salivary  corpuscles,  155,  157 
Salivary  glands,  171 

blood-vessels  of,  173 

demilunes,  171 

excretory  ducts  of,  171,  172 

intercalated  tubules,  171 

intralobular  tubes,  172 

membrana  propria  of,  171 

mixed,  171 

mucous,  171 

nerves  of,  173 

rod  epithelium  of,  171 

secreting  cells  of,  171,  172 

serous,  171 
Salt  solution,  normal,  19 
Sarcolemma,  75,  279 
Sarcoplasm,  74 
Sarcostyles,  74 
Sarcous  elements,  74 
Schmidt-Lantermann  segments,  82 
Sclera.  23S 
Sebaceous  glands,  231,  315 

distribution  of,  232 

secretion  of,  232 
Secretory  capillaries,  62,  160 
Sectioning,  30,  329 
Sections,  preservation  of.  330 
Segments,  cylindro-conical,  82 

internodal,  73 

medullary,  82 

Schmidt-Lantermann,  82 


Semen,  201 

elements  of,  312 
Semicircular  canals,  260 

ampuUoe  of,  260 

crista;  acusticLU,  260 
Seminal  filaments  of  frog,  312 

vesicles,  203,  313 
Seminiferous  tubules,  312 
Septula  medullaria,  117 
Sertoli's  columns,  200 
Sharpey's  fibers,  71,  104,  148 
Silver  nitrate,  20,  21 
Sinus  lactiferus,  234 
Sister-loops,  53 
Skin,  223 

arrector  pili,  227 

blood-vessels  of,  223,  316 

coil-glands,  232,  314 

color  of,  225,  226 

corium,  223 

cuticle,  223 

derma,  223 

eleidin  granules,  224 

epidermis,  223 

glands  of,  23 1 

hair,  227 

hair-follicles,  228 

lymph-vessels  of,  233 

nails,  226 

nerves  of,  233 

panniculus  adiposus,  223 

papillae  of,  223 

pigment  of,  225 

rete  mucosum,  224 

sebaceous  glands,  232 

stratum  corneum,  224 

stratum  granulosum,  224 

stratum  lucidum,  225 

stratum  Malpighii,  224 

stratum  papillare,  223 

stratum  reticulare,  223 

stratum  subcutaneum,  223 

striated  muscle-fibers  of,  224 
Slides,  18 
Smooth  muscle,  72 
Sodium  carminate,  23 

hyposulphite,  20 
Solitary  follicles,  166 
Spaces  of  Fontana,  242 

of  Nuel,  266 
Spermatids,  200 
Spermatogenesis,  200 
Spermatozoa,  201 
Spinal  cord,  116,  293 

anterior  column,  1 16 

anterior  cornua,  I16 

anterior  gray  commissure,  117 

anterior  medi.in  fissure,  116 

anterior  roots  of  nerves  of,  116 

central  canal,  1 17 

collateral  fibers,  1 18,  119,  120 

column  of  Burdach,  :i6 

column-cells,  1 18 

column  of  Clark,  116,  119,  I20 

column  of  GoU,  II6 

commissure-cells,    118 

conus  medullaris,  117 


343 


Spinal  cord,  Dciters's  cells,  122 

dorsal  nucleus,  Il6 

epcndymal  cells,  122 

funiculus  cuneatus,  Il6 

funiculus  gracilis,  Il6 

glia-cells,  122 

(jolgi's  method  of  staining,  294 

gray  commissure,  116 

gray  substance  of,  117 

interior  cells,  120 

lateral  column,  116 

lateral  cumua,  116 

motor  nerve-cells,  llS 

multipolar  ganglion-cells,  2S1 

nerve-fibers  of,  120 

neuroglia,  117,  122 

posterior  column,  116 

posterior comua,  Ii6 

l>osterior  gray  commissure  of,  117 

iwsterior  roots  of  nerves  of,  1 16 

posterior  septum,  116 

pluricordonal  cells,  120 

reticular  process,  116 

septula  meduUaria,  117 

stem-fiber,  118 

staining  of  axis-cylinders  of,  294 

staining  of  cells  of,  294 

staining  of  medullated  fibers  of,  294 

sul>stantia  gelatinosa  centralis,  1 23 

substantia    gelatinosa  Rolandi,  123 

white  commissure,  116 

white  substance  of,  121 

zona  spongiosa,  117 

zona  terminalis,  1 17 
Spiral  organ,  263 
Spleen,  97,  288 

blood-vessels  of,  99,  288 

capsule  of,  97 

elements  of,  288 

intermediate  lacuna',  lOO 

karyomitotic  figures  in,  288 

lymphatics  of,  100 

Malpighian  corpuscles  of,  98 

pulp  of,  97 

reticular  connective  tissue  of,  288 

trabecula-  of,  97 
Spongioplasm,  48 
Stage-micrometer,  45 
Staining,  31 

bulk,  32 

diffuse,  32 

double,  i^ 

gold,  37 

mucous,  34 

nuclear,  31,  33 

silver,  35 

triple,  34 

under  the  cover-glass,  41 
Stomach,  158,  302 

Auerbach's  plexus,  170 

bloodvessels  of,  168,  305 

epithelium  of,  isolated,  302 

glanils  of,  160,  302 

lymph-vessels  of,  169 

Meissner's  plexus,  170 

nmcous  membrane  of,  302 

muscular  tissue  of,  162 


Stomach,  ner\es  of,  170 
Strangzellen,  liS 
Strata  of  skin,  314 
Striated  muscle,  73 
Sublingual  gland,  171,  306 
Submaxillary,  171,  306 
Substantia  compacta,  loo 

gelatinosa  centralis,  1 1 7,  123 

gelatinosa  Rolandi,  117,  123 

propria,  237 

spongiosa,  of  bone,  loi 
Sudoriparous  glands,  232 
Suprarenal  body,  143,  299,  300 

blood-vessels  of,  144 

elements  of,  300 

nerves  of,  144 

zona  fasciculati,  1 43 

zona  glomerulosa,  143 

zona  reticularis,  143 
Sutures,  105 
Svk-eat-glands,  232 
Synarthroses,  105 
Synchondrosis,  105 
Syncytium,  220 
Syndesmosis,  105 
Synovial  membranes,  105 

villi,  105,  291 


Tactile-cells,  compound,  139,  298 

simple,  139,  297 
Tapetum  cellulosuin,  239 

tibrosum,  239 
Taste-buds,  154,  185,  273,  324,  325 

gustatory  cells,  274 

ner\'es  of,  325 

orientation  of,  324 

taste-pore,  273 

tegmental  cells,  274 
Teasing,  25 
Teeth,  146,  300 

blood-vessels  of,  148 

cementum,  146,  148,  151 

crown,  146 

dental  bulb,  148 

dental  furrow,  149 

dental  papilla,  14S 

dental  ridge,  148 

dental  sack,  151 

dentinal  fibers,  147,  14S 

dentinal  globules,  147 

dentinal  sheath,  147 

dentinal  tubules,  147 

dentine,  146 

development  of,  148,  301 

dried,  300 

enamel,  146 

enamel  cuticle,  151 

enamel  organ,  149 

enamel  prisms,  300 

epithelial  sheath,  150 

fang,  146 

interglobular  spaces,  147 

isthmus,  149 

neck,  146 

nerves  of,  148 


344 


Teeth,  odontoblasts,  148,  150 

pulp  of,  146,  14S 
Telre  choroide;!:,  133 
Tendon,  1 13,  1 14,  292,  293 

cells  of,  293 
Tendon-sheath,  113,  115 
Tendon-spindles,  1 15 
Tenon's  space,  255 
Terminal  bronchioles,  1S5 

vesicles,  186 
Testicle,  198,  311 

blood-vessels  of,  201 

cells  of,  200 

corpus  Highniori,  199 

ducts  of,  202 

elements  of,  312 

hydatids  of,  204 

lobules  of,  198 

lymph-vessels  of,  201 

mediastinum  of,  199 

nerves  of,  201 

rete  testis,  199 

secretion  of,  201 

seminiferous  tubules,  199 

Sertoli's  columns,  200 

tubuli  recti,  200 

tunica  albuginea  of,  19S 

tunica  vasculosi  of,  199 
Thymus  body,  190,  310 

blood-vessels  of,  191 

corpuscles  of  Hassall,  190 
Thyro-glossalduct,  189 
Thyroid  gland,  61,  189,  309 

duct  of.  189 

colloid  substance  of,  189 
Tissue  juices,  72,  94 
Tissues,  47 

animal,  48 

vegetative,  47 
Tongue,  153,  301 

blood-vessels  of,  156 

glands  of,  155 

lymph-follicles  of,  154,  301 

lymph-vessels  of,  156 

mucosa  of,  153 

muscles  of,  153 

nerves  of  156 

papilla:  of,  153,  301 
•ronsils,  157,  301  " 
Trachea,  185 

cartilages  of,  1 85 

elastic  fibers  of,  185 

glands  of,  1 85 
Transitional  epithelium,  296 
Triacid  solution,  2S5 
Tympanum,  268 


U. 

Ureters,  196,  311 

transitional  epithelium  of,  19 
Urethra,  198,  311,  313 

blood-vessels  of,  19S 

female,  198 

glands  of,  198 

male,  198, 

papillce  of,  19S 


Urinary  bladder,  197,  311 

internal  vesical  sphincter,  197 

Urogenital  sinus,  198 

Uterus,  210,  313 

blood-vessels  of,  213,  215,  216 

cervix,  213 

decidual  cells,  216 

glands  of,  212 

lymph-vessels  of,  217 

mucosa  of  the  gravid,  215 

mucosa  of  the  menstruating,  214 

mucosa  of  the  virgin  resting,  212 

mucous  crypts,  213 

nerves  of,  217 

ovula  Nabothi,  214 

Utricle,  260 


Vagina,  222 

blood-vessels  of,  223 

lymph -vessels  of,  223 

secretion  of,  223 

tunics  of,  222 
Valvula;  conniventes,  162  * 

Vas  aberrans  Halleri,  204 
Vas  deferens,  203,  313 

ampulla  of,  203 
Vasa  aberrantia,  174 

efierentia,  202 

vasorum,  90 
Vasoformative  cells,  284 
Vater's  corpuscles,  140 
Veins,  88 

valves  of,  89 
Ventricle  of  Morgagni,  1S4 
Vesuvin,  23,  33 
Vicq  d'Azyr's  bundle,  126 
Villi  of  arachnoid,  133 

of  intestine,  small,  162 

of  placenta,  217 

synovial,  106,  291 
Vitellus,  208 
Vitreous  body,  236 
Vocal  cords,  184 
Volkmann's  canals,  102 
Voluntary  muscle,  73 

W. 

Wagner  and  Meissner's  corpuscles,  i 
Wandering  cells,  91,  238 

hematogenetic,  67 

histogenetic,  67 
Westphal's  alum-carmine  dahlia,  23 


Xylol,  21 

-balsam,  22 


Zell-knoten,  220 
Zona  pellucida,  .207 
Zone  of  Zinn,  252 
Zonula  ciliaris,  252 
Zymogen  granules,  172 


COLUMBIA  UNIVERSITY  LIBRARY 

This  book  is  due  on  the  date  indicated  below,  or  at  the 
expiration  of  a  definite  period  after  the  date  of  borrowing, 
as  provided  by  the  rules  of  the  Library  or  by  special  ar- 
rangement with  the  Librarian  in  charge. 

DATE  BORROWEO 

DATE  DUE 

DATE  BORROWED 

DATE  DUE 

194S 

•m  - 

c2el29e)Mioo 

.i:.!551 
Stohr 

St61 
1896 

/  Text-book  of  histology 

1 

